diff --git a/db/migrations/20260411182550_template_defaults.sql b/db/migrations/20260411182550_template_defaults.sql
new file mode 100644
index 0000000..3378453
--- /dev/null
+++ b/db/migrations/20260411182550_template_defaults.sql
@@ -0,0 +1,17 @@
+-- +goose Up
+ALTER TABLE templates
+    ADD COLUMN default_user TEXT NOT NULL DEFAULT 'root',
+    ADD COLUMN default_env  JSONB NOT NULL DEFAULT '{}';
+
+ALTER TABLE template_builds
+    ADD COLUMN default_user TEXT NOT NULL DEFAULT 'root',
+    ADD COLUMN default_env  JSONB NOT NULL DEFAULT '{}';
+
+-- +goose Down
+ALTER TABLE template_builds
+    DROP COLUMN default_env,
+    DROP COLUMN default_user;
+
+ALTER TABLE templates
+    DROP COLUMN default_env,
+    DROP COLUMN default_user;
diff --git a/db/queries/template_builds.sql b/db/queries/template_builds.sql
index 1fb07be..1a0e3b0 100644
--- a/db/queries/template_builds.sql
+++ b/db/queries/template_builds.sql
@@ -31,3 +31,8 @@ WHERE id = $1;
 UPDATE template_builds
 SET error = $2, status = 'failed', completed_at = NOW()
 WHERE id = $1;
+
+-- name: UpdateBuildDefaults :exec
+UPDATE template_builds
+SET default_user = $2, default_env = $3
+WHERE id = $1;
diff --git a/db/queries/templates.sql b/db/queries/templates.sql
index de4d6f2..fbea228 100644
--- a/db/queries/templates.sql
+++ b/db/queries/templates.sql
@@ -1,6 +1,6 @@
 -- name: InsertTemplate :one
-INSERT INTO templates (id, name, type, vcpus, memory_mb, size_bytes, team_id)
-VALUES ($1, $2, $3, $4, $5, $6, $7)
+INSERT INTO templates (id, name, type, vcpus, memory_mb, size_bytes, team_id, default_user, default_env)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
 RETURNING *;
 
 -- name: GetTemplate :one
diff --git a/frontend/src/lib/api/builds.ts b/frontend/src/lib/api/builds.ts
index 1de23b8..fe9fa1f 100644
--- a/frontend/src/lib/api/builds.ts
+++ b/frontend/src/lib/api/builds.ts
@@ -1,4 +1,4 @@
-import { apiFetch, type ApiResult } from '$lib/api/client';
+import { apiFetch, apiFetchMultipart, type ApiResult } from '$lib/api/client';
 
 export type BuildLogEntry = {
 	step: number;
@@ -26,6 +26,8 @@ export type Build = {
 	error?: string;
 	sandbox_id?: string;
 	host_id?: string;
+	default_user: string;
+	default_env: Record<string, string>;
 	created_at: string;
 	started_at?: string;
 	completed_at?: string;
@@ -39,9 +41,18 @@ export type CreateBuildParams = {
 	vcpus?: number;
 	memory_mb?: number;
 	skip_pre_post?: boolean;
+	archive?: File;
 };
 
 export async function createBuild(params: CreateBuildParams): Promise<ApiResult<Build>> {
+	if (params.archive) {
+		// Use multipart when an archive file is provided.
+		const { archive, ...config } = params;
+		const formData = new FormData();
+		formData.append('config', JSON.stringify(config));
+		formData.append('archive', archive);
+		return apiFetchMultipart('POST', '/api/v1/admin/builds', formData);
+	}
 	return apiFetch('POST', '/api/v1/admin/builds', params);
 }
 
diff --git a/frontend/src/lib/api/client.ts b/frontend/src/lib/api/client.ts
index 00fa381..d6e6459 100644
--- a/frontend/src/lib/api/client.ts
+++ b/frontend/src/lib/api/client.ts
@@ -22,3 +22,24 @@ export async function apiFetch<T>(method: string, path: string, body?: unknown):
 		return { ok: false, error: 'Unable to connect to the server' };
 	}
 }
+
+export async function apiFetchMultipart<T>(method: string, path: string, formData: FormData): Promise<ApiResult<T>> {
+	try {
+		const headers: Record<string, string> = {};
+		if (auth.token) headers['Authorization'] = `Bearer ${auth.token}`;
+
+		const res = await fetch(path, {
+			method,
+			headers,
+			body: formData
+		});
+
+		if (res.status === 204) return { ok: true, data: undefined as T };
+
+		const data = await res.json();
+		if (!res.ok) return { ok: false, error: data?.error?.message ?? 'Something went wrong' };
+		return { ok: true, data: data as T };
+	} catch {
+		return { ok: false, error: 'Unable to connect to the server' };
+	}
+}
diff --git a/frontend/src/lib/components/AdminSidebar.svelte b/frontend/src/lib/components/AdminSidebar.svelte
index ebf4b64..d01e857 100644
--- a/frontend/src/lib/components/AdminSidebar.svelte
+++ b/frontend/src/lib/components/AdminSidebar.svelte
@@ -22,8 +22,8 @@
 	};
 
 	const managementItems: NavItem[] = [
-		{ label: 'Hosts', icon: IconServer, href: '/admin/hosts' },
-		{ label: 'Templates', icon: IconTemplate, href: '/admin/templates' }
+		{ label: 'Templates', icon: IconTemplate, href: '/admin/templates' },
+		{ label: 'Hosts', icon: IconServer, href: '/admin/hosts' }
 	];
 
 	function isActive(href: string): boolean {
diff --git a/frontend/src/routes/admin/+page.svelte b/frontend/src/routes/admin/+page.svelte
index b5a56c1..c6c45dc 100644
--- a/frontend/src/routes/admin/+page.svelte
+++ b/frontend/src/routes/admin/+page.svelte
@@ -1,5 +1,5 @@
 <script lang="ts">
 	import { goto } from '$app/navigation';
 	import { onMount } from 'svelte';
-	onMount(() => goto('/admin/hosts', { replaceState: true }));
+	onMount(() => goto('/admin/templates', { replaceState: true }));
 </script>
diff --git a/frontend/src/routes/admin/templates/+page.svelte b/frontend/src/routes/admin/templates/+page.svelte
index 39b62da..67c3b0a 100644
--- a/frontend/src/routes/admin/templates/+page.svelte
+++ b/frontend/src/routes/admin/templates/+page.svelte
@@ -56,7 +56,8 @@
 		memory_mb: 512,
 		recipe: '',
 		healthcheck: '',
-		skip_pre_post: false
+		skip_pre_post: false,
+		archive: null as File | null
 	});
 	let creating = $state(false);
 	let createError = $state<string | null>(null);
@@ -131,12 +132,13 @@
 			healthcheck: createForm.healthcheck.trim() || undefined,
 			vcpus: createForm.vcpus,
 			memory_mb: createForm.memory_mb,
-			skip_pre_post: createForm.skip_pre_post
+			skip_pre_post: createForm.skip_pre_post,
+			archive: createForm.archive || undefined
 		});
 
 		if (result.ok) {
 			showCreate = false;
-			createForm = { name: '', base_template: 'minimal', vcpus: 1, memory_mb: 512, recipe: '', healthcheck: '', skip_pre_post: false };
+			createForm = { name: '', base_template: 'minimal', vcpus: 1, memory_mb: 512, recipe: '', healthcheck: '', skip_pre_post: false, archive: null };
 			builds = [result.data, ...builds];
 			activeTab = 'builds';
 			expandedBuildId = result.data.id;
@@ -235,6 +237,8 @@
 			case 'RUN':     return 'var(--color-blue)';
 			case 'START':   return 'var(--color-accent-bright)';
 			case 'ENV':     return 'var(--color-amber)';
+			case 'USER':    return 'var(--color-accent)';
+			case 'COPY':    return 'var(--color-text-bright)';
 			case 'WORKDIR': return 'var(--color-text-tertiary)';
 			default:        return 'var(--color-text-muted)';
 		}
@@ -277,7 +281,7 @@
 					</p>
 				</div>
 				<button
-					onclick={() => { showCreate = true; createError = null; createForm = { name: '', base_template: 'minimal', vcpus: 1, memory_mb: 512, recipe: '', healthcheck: '', skip_pre_post: false }; }}
+					onclick={() => { showCreate = true; createError = null; createForm = { name: '', base_template: 'minimal', vcpus: 1, memory_mb: 512, recipe: '', healthcheck: '', skip_pre_post: false, archive: null }; }}
 					class="flex items-center gap-2 rounded-[var(--radius-button)] bg-[var(--color-accent)] px-4 py-2 text-ui font-semibold text-white shadow-sm transition-all duration-150 hover:brightness-115 hover:-translate-y-px active:translate-y-0"
 				>
 					<svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"><line x1="12" y1="5" x2="12" y2="19"/><line x1="5" y1="12" x2="19" y2="12"/></svg>
@@ -608,7 +612,7 @@
 															<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="var(--color-red)" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round" class="shrink-0"><line x1="18" y1="6" x2="6" y2="18"/><line x1="6" y1="6" x2="18" y2="18"/></svg>
 														{/if}
 														<span class="shrink-0 text-label font-semibold text-[var(--color-text-tertiary)]">{phaseLabel}</span>
-														<code class="flex-1 truncate font-mono text-meta"><span style="color: {keywordColor(kw)}">{kw}</span>{#if kwRest}<span class="text-[var(--color-text-secondary)]"> {kwRest}</span>{/if}</code>
+														<code class="flex-1 truncate font-mono text-meta"><span style="color: {keywordColor(kw)}">{kw}</span>{#if kwRest}{' '}<span class="text-[var(--color-text-secondary)]">{kwRest}</span>{/if}</code>
 														<span class="shrink-0 font-mono text-label text-[var(--color-text-muted)]">{log.elapsed_ms}ms</span>
 														{#if log.exit !== 0}
 															<span class="shrink-0 rounded-full bg-[var(--color-red)]/10 px-1.5 py-0.5 font-mono text-label text-[var(--color-red)]">
@@ -661,13 +665,16 @@
 									<!-- Recipe reference -->
 									{#if build.recipe && build.recipe.length > 0}
 										<div class="mt-4 border-t border-[var(--color-border)] pt-4">
-											<span class="text-label font-semibold uppercase tracking-[0.06em] text-[var(--color-text-tertiary)]">Recipe</span>
+											<div class="flex items-center gap-1.5">
+												<span class="text-label font-semibold uppercase tracking-[0.06em] text-[var(--color-text-tertiary)]">Recipe</span>
+												<CopyButton value={build.recipe.join('\n')} />
+											</div>
 											<div class="mt-2 rounded-[var(--radius-input)] bg-[var(--color-bg-1)] border border-[var(--color-border)] px-3 py-2">
 												{#each build.recipe as cmd, i}
 													{@const [kw, kwRest] = splitInstruction(cmd)}
 													<div class="flex gap-2 py-0.5">
 														<span class="shrink-0 font-mono text-label text-[var(--color-text-muted)] tabular-nums">{i + 1}.</span>
-														<code class="font-mono text-meta"><span style="color: {keywordColor(kw)}">{kw}</span>{#if kwRest}<span class="text-[var(--color-text-secondary)]"> {kwRest}</span>{/if}</code>
+														<code class="font-mono text-meta"><span style="color: {keywordColor(kw)}">{kw}</span>{#if kwRest}{' '}<span class="text-[var(--color-text-secondary)]">{kwRest}</span>{/if}</code>
 													</div>
 												{/each}
 											</div>
@@ -787,10 +794,45 @@
 						class="w-full resize-y rounded-[var(--radius-input)] border border-[var(--color-border)] bg-[var(--color-bg-4)] px-3 py-2 font-mono text-meta leading-relaxed text-[var(--color-text-bright)] outline-none placeholder:text-[var(--color-text-muted)] transition-colors duration-150 focus:border-[var(--color-accent)] disabled:opacity-60"
 					></textarea>
 					<p class="mt-1 text-label text-[var(--color-text-muted)]">
-						Supports <code class="font-mono">RUN</code>, <code class="font-mono">START</code>, <code class="font-mono">WORKDIR</code>, <code class="font-mono">ENV key=value</code>. RUN steps have a 30s timeout; override with <code class="font-mono">RUN --timeout=5m</code>.
+						Supports <code class="font-mono">RUN</code>, <code class="font-mono">START</code>, <code class="font-mono">WORKDIR</code>, <code class="font-mono">ENV key=value</code>, <code class="font-mono">USER name</code>, <code class="font-mono">COPY src dst</code>. RUN steps have a 30s timeout; override with <code class="font-mono">RUN --timeout=5m</code>. COPY references files from the uploaded archive.
 					</p>
 				</div>
 
+				<div>
+					<label class="mb-1.5 block text-label font-semibold uppercase tracking-[0.05em] text-[var(--color-text-tertiary)]" for="tmpl-archive">
+						Build Archive <span class="normal-case font-normal text-[var(--color-text-muted)]">(optional, for COPY commands)</span>
+					</label>
+					<div class="flex items-center gap-3">
+						<label
+							class="flex cursor-pointer items-center gap-2 rounded-[var(--radius-button)] border border-[var(--color-border)] bg-[var(--color-bg-4)] px-3 py-2 text-ui text-[var(--color-text-secondary)] transition-colors duration-150 hover:border-[var(--color-border-mid)] hover:text-[var(--color-text-primary)]"
+						>
+							<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4"/><polyline points="17 8 12 3 7 8"/><line x1="12" y1="3" x2="12" y2="15"/></svg>
+							Choose file
+							<input
+								id="tmpl-archive"
+								type="file"
+								accept=".tar,.tar.gz,.tgz,.zip"
+								disabled={creating}
+								onchange={(e) => { const f = (e.target as HTMLInputElement).files?.[0]; createForm.archive = f ?? null; }}
+								class="hidden"
+							/>
+						</label>
+						{#if createForm.archive}
+							<span class="flex items-center gap-1.5 text-meta text-[var(--color-text-secondary)]">
+								<span class="font-mono">{createForm.archive.name}</span>
+								<button
+									onclick={() => { createForm.archive = null; }}
+									class="text-[var(--color-text-muted)] hover:text-[var(--color-red)] transition-colors"
+								>
+									<svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"><line x1="18" y1="6" x2="6" y2="18"/><line x1="6" y1="6" x2="18" y2="18"/></svg>
+								</button>
+							</span>
+						{:else}
+							<span class="text-meta text-[var(--color-text-muted)]">tar, tar.gz, or zip</span>
+						{/if}
+					</div>
+				</div>
+
 				<div>
 					<label class="mb-1.5 block text-label font-semibold uppercase tracking-[0.05em] text-[var(--color-text-tertiary)]" for="tmpl-healthcheck">
 						Healthcheck <span class="normal-case font-normal text-[var(--color-text-muted)]">(optional)</span>
diff --git a/internal/api/handlers_builds.go b/internal/api/handlers_builds.go
index bd3260e..b0b0e40 100644
--- a/internal/api/handlers_builds.go
+++ b/internal/api/handlers_builds.go
@@ -3,8 +3,10 @@ package api
 import (
 	"encoding/json"
 	"fmt"
+	"io"
 	"log/slog"
 	"net/http"
+	"strings"
 	"time"
 
 	"connectrpc.com/connect"
@@ -54,6 +56,8 @@ type buildResponse struct {
 	Error        *string         `json:"error,omitempty"`
 	SandboxID    *string         `json:"sandbox_id,omitempty"`
 	HostID       *string         `json:"host_id,omitempty"`
+	DefaultUser  string          `json:"default_user"`
+	DefaultEnv   json.RawMessage `json:"default_env"`
 	CreatedAt    string          `json:"created_at"`
 	StartedAt    *string         `json:"started_at,omitempty"`
 	CompletedAt  *string         `json:"completed_at,omitempty"`
@@ -71,6 +75,8 @@ func buildToResponse(b db.TemplateBuild) buildResponse {
 		CurrentStep:  b.CurrentStep,
 		TotalSteps:   b.TotalSteps,
 		Logs:         b.Logs,
+		DefaultUser:  b.DefaultUser,
+		DefaultEnv:   b.DefaultEnv,
 	}
 	if b.Healthcheck != "" {
 		resp.Healthcheck = &b.Healthcheck
@@ -101,11 +107,54 @@ func buildToResponse(b db.TemplateBuild) buildResponse {
 }
 
 // Create handles POST /v1/admin/builds.
+// Accepts either JSON body or multipart/form-data with a "config" JSON part
+// and an optional "archive" file part (tar/tar.gz/zip for COPY commands).
 func (h *buildHandler) Create(w http.ResponseWriter, r *http.Request) {
 	var req createBuildRequest
-	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		writeError(w, http.StatusBadRequest, "invalid_request", "invalid JSON body")
-		return
+	var archive []byte
+	var archiveName string
+
+	ct := r.Header.Get("Content-Type")
+	if strings.HasPrefix(ct, "multipart/") {
+		// 100 MB max for multipart (archive + JSON config).
+		if err := r.ParseMultipartForm(100 << 20); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid_request", "failed to parse multipart form")
+			return
+		}
+
+		// Parse JSON config from "config" field.
+		configStr := r.FormValue("config")
+		if configStr == "" {
+			writeError(w, http.StatusBadRequest, "invalid_request", "multipart form requires a 'config' JSON field")
+			return
+		}
+		if err := json.Unmarshal([]byte(configStr), &req); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid_request", "invalid config JSON in multipart form")
+			return
+		}
+
+		// Read optional archive file (max 100 MB).
+		file, header, err := r.FormFile("archive")
+		if err == nil {
+			defer file.Close()
+			const maxArchiveSize = 100 << 20 // 100 MB
+			lr := io.LimitReader(file, maxArchiveSize+1)
+			archive, err = io.ReadAll(lr)
+			if err != nil {
+				writeError(w, http.StatusBadRequest, "invalid_request", "failed to read archive file")
+				return
+			}
+			if int64(len(archive)) > maxArchiveSize {
+				writeError(w, http.StatusRequestEntityTooLarge, "invalid_request", "archive exceeds 100 MB limit")
+				return
+			}
+			archiveName = header.Filename
+		}
+	} else {
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid_request", "invalid JSON body")
+			return
+		}
 	}
 
 	if req.Name == "" {
@@ -129,6 +178,8 @@ func (h *buildHandler) Create(w http.ResponseWriter, r *http.Request) {
 		VCPUs:        req.VCPUs,
 		MemoryMB:     req.MemoryMB,
 		SkipPrePost:  req.SkipPrePost,
+		Archive:      archive,
+		ArchiveName:  archiveName,
 	})
 	if err != nil {
 		slog.Error("failed to create build", "error", err)
diff --git a/internal/api/handlers_snapshots.go b/internal/api/handlers_snapshots.go
index 8855c29..df3c6ef 100644
--- a/internal/api/handlers_snapshots.go
+++ b/internal/api/handlers_snapshots.go
@@ -210,13 +210,15 @@ func (h *snapshotHandler) Create(w http.ResponseWriter, r *http.Request) {
 	}
 
 	tmpl, err := h.db.InsertTemplate(snapCtx, db.InsertTemplateParams{
-		ID:        newTemplateID,
-		Name:      req.Name,
-		Type:      "snapshot",
-		Vcpus:     sb.Vcpus,
-		MemoryMb:  sb.MemoryMb,
-		SizeBytes: resp.Msg.SizeBytes,
-		TeamID:    ac.TeamID,
+		ID:          newTemplateID,
+		Name:        req.Name,
+		Type:        "snapshot",
+		Vcpus:       sb.Vcpus,
+		MemoryMb:    sb.MemoryMb,
+		SizeBytes:   resp.Msg.SizeBytes,
+		TeamID:      ac.TeamID,
+		DefaultUser: "root",
+		DefaultEnv:  []byte("{}"),
 	})
 	if err != nil {
 		slog.Error("failed to insert template record", "name", req.Name, "error", err)
diff --git a/internal/db/models.go b/internal/db/models.go
index 3b9cd9e..45c00da 100644
--- a/internal/db/models.go
+++ b/internal/db/models.go
@@ -152,14 +152,16 @@ type TeamApiKey struct {
 }
 
 type Template struct {
-	Name      string             `json:"name"`
-	Type      string             `json:"type"`
-	Vcpus     int32              `json:"vcpus"`
-	MemoryMb  int32              `json:"memory_mb"`
-	SizeBytes int64              `json:"size_bytes"`
-	CreatedAt pgtype.Timestamptz `json:"created_at"`
-	TeamID    pgtype.UUID        `json:"team_id"`
-	ID        pgtype.UUID        `json:"id"`
+	Name        string             `json:"name"`
+	Type        string             `json:"type"`
+	Vcpus       int32              `json:"vcpus"`
+	MemoryMb    int32              `json:"memory_mb"`
+	SizeBytes   int64              `json:"size_bytes"`
+	CreatedAt   pgtype.Timestamptz `json:"created_at"`
+	TeamID      pgtype.UUID        `json:"team_id"`
+	ID          pgtype.UUID        `json:"id"`
+	DefaultUser string             `json:"default_user"`
+	DefaultEnv  []byte             `json:"default_env"`
 }
 
 type TemplateBuild struct {
@@ -183,6 +185,8 @@ type TemplateBuild struct {
 	TemplateID   pgtype.UUID        `json:"template_id"`
 	TeamID       pgtype.UUID        `json:"team_id"`
 	SkipPrePost  bool               `json:"skip_pre_post"`
+	DefaultUser  string             `json:"default_user"`
+	DefaultEnv   []byte             `json:"default_env"`
 }
 
 type User struct {
diff --git a/internal/db/template_builds.sql.go b/internal/db/template_builds.sql.go
index facfb19..ff15634 100644
--- a/internal/db/template_builds.sql.go
+++ b/internal/db/template_builds.sql.go
@@ -12,7 +12,7 @@ import (
 )
 
 const getTemplateBuild = `-- name: GetTemplateBuild :one
-SELECT id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post FROM template_builds WHERE id = $1
+SELECT id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post, default_user, default_env FROM template_builds WHERE id = $1
 `
 
 func (q *Queries) GetTemplateBuild(ctx context.Context, id pgtype.UUID) (TemplateBuild, error) {
@@ -39,6 +39,8 @@ func (q *Queries) GetTemplateBuild(ctx context.Context, id pgtype.UUID) (Templat
 		&i.TemplateID,
 		&i.TeamID,
 		&i.SkipPrePost,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
@@ -46,7 +48,7 @@ func (q *Queries) GetTemplateBuild(ctx context.Context, id pgtype.UUID) (Templat
 const insertTemplateBuild = `-- name: InsertTemplateBuild :one
 INSERT INTO template_builds (id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, total_steps, template_id, team_id, skip_pre_post)
 VALUES ($1, $2, $3, $4, $5, $6, $7, 'pending', $8, $9, $10, $11)
-RETURNING id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post
+RETURNING id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post, default_user, default_env
 `
 
 type InsertTemplateBuildParams struct {
@@ -99,12 +101,14 @@ func (q *Queries) InsertTemplateBuild(ctx context.Context, arg InsertTemplateBui
 		&i.TemplateID,
 		&i.TeamID,
 		&i.SkipPrePost,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const listTemplateBuilds = `-- name: ListTemplateBuilds :many
-SELECT id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post FROM template_builds ORDER BY created_at DESC
+SELECT id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post, default_user, default_env FROM template_builds ORDER BY created_at DESC
 `
 
 func (q *Queries) ListTemplateBuilds(ctx context.Context) ([]TemplateBuild, error) {
@@ -137,6 +141,8 @@ func (q *Queries) ListTemplateBuilds(ctx context.Context) ([]TemplateBuild, erro
 			&i.TemplateID,
 			&i.TeamID,
 			&i.SkipPrePost,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
@@ -148,6 +154,23 @@ func (q *Queries) ListTemplateBuilds(ctx context.Context) ([]TemplateBuild, erro
 	return items, nil
 }
 
+const updateBuildDefaults = `-- name: UpdateBuildDefaults :exec
+UPDATE template_builds
+SET default_user = $2, default_env = $3
+WHERE id = $1
+`
+
+type UpdateBuildDefaultsParams struct {
+	ID          pgtype.UUID `json:"id"`
+	DefaultUser string      `json:"default_user"`
+	DefaultEnv  []byte      `json:"default_env"`
+}
+
+func (q *Queries) UpdateBuildDefaults(ctx context.Context, arg UpdateBuildDefaultsParams) error {
+	_, err := q.db.Exec(ctx, updateBuildDefaults, arg.ID, arg.DefaultUser, arg.DefaultEnv)
+	return err
+}
+
 const updateBuildError = `-- name: UpdateBuildError :exec
 UPDATE template_builds
 SET error = $2, status = 'failed', completed_at = NOW()
@@ -204,7 +227,7 @@ SET status = $2,
     started_at   = CASE WHEN $2 = 'running'   AND started_at   IS NULL THEN NOW() ELSE started_at   END,
     completed_at = CASE WHEN $2 IN ('success', 'failed', 'cancelled') THEN NOW() ELSE completed_at END
 WHERE id = $1
-RETURNING id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post
+RETURNING id, name, base_template, recipe, healthcheck, vcpus, memory_mb, status, current_step, total_steps, logs, error, sandbox_id, host_id, created_at, started_at, completed_at, template_id, team_id, skip_pre_post, default_user, default_env
 `
 
 type UpdateBuildStatusParams struct {
@@ -236,6 +259,8 @@ func (q *Queries) UpdateBuildStatus(ctx context.Context, arg UpdateBuildStatusPa
 		&i.TemplateID,
 		&i.TeamID,
 		&i.SkipPrePost,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
diff --git a/internal/db/templates.sql.go b/internal/db/templates.sql.go
index 7d37808..1606d6f 100644
--- a/internal/db/templates.sql.go
+++ b/internal/db/templates.sql.go
@@ -45,7 +45,7 @@ func (q *Queries) DeleteTemplatesByTeam(ctx context.Context, teamID pgtype.UUID)
 }
 
 const getPlatformTemplateByName = `-- name: GetPlatformTemplateByName :one
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE team_id = '00000000-0000-0000-0000-000000000000' AND name = $1
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE team_id = '00000000-0000-0000-0000-000000000000' AND name = $1
 `
 
 // Check if a global (platform) template exists with the given name.
@@ -61,12 +61,14 @@ func (q *Queries) GetPlatformTemplateByName(ctx context.Context, name string) (T
 		&i.CreatedAt,
 		&i.TeamID,
 		&i.ID,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const getTemplate = `-- name: GetTemplate :one
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE id = $1
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE id = $1
 `
 
 func (q *Queries) GetTemplate(ctx context.Context, id pgtype.UUID) (Template, error) {
@@ -81,12 +83,14 @@ func (q *Queries) GetTemplate(ctx context.Context, id pgtype.UUID) (Template, er
 		&i.CreatedAt,
 		&i.TeamID,
 		&i.ID,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const getTemplateByName = `-- name: GetTemplateByName :one
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE team_id = $1 AND name = $2
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE team_id = $1 AND name = $2
 `
 
 type GetTemplateByNameParams struct {
@@ -107,12 +111,14 @@ func (q *Queries) GetTemplateByName(ctx context.Context, arg GetTemplateByNamePa
 		&i.CreatedAt,
 		&i.TeamID,
 		&i.ID,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const getTemplateByTeam = `-- name: GetTemplateByTeam :one
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE name = $1 AND (team_id = $2 OR team_id = '00000000-0000-0000-0000-000000000000')
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE name = $1 AND (team_id = $2 OR team_id = '00000000-0000-0000-0000-000000000000')
 `
 
 type GetTemplateByTeamParams struct {
@@ -133,24 +139,28 @@ func (q *Queries) GetTemplateByTeam(ctx context.Context, arg GetTemplateByTeamPa
 		&i.CreatedAt,
 		&i.TeamID,
 		&i.ID,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const insertTemplate = `-- name: InsertTemplate :one
-INSERT INTO templates (id, name, type, vcpus, memory_mb, size_bytes, team_id)
-VALUES ($1, $2, $3, $4, $5, $6, $7)
-RETURNING name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id
+INSERT INTO templates (id, name, type, vcpus, memory_mb, size_bytes, team_id, default_user, default_env)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
+RETURNING name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env
 `
 
 type InsertTemplateParams struct {
-	ID        pgtype.UUID `json:"id"`
-	Name      string      `json:"name"`
-	Type      string      `json:"type"`
-	Vcpus     int32       `json:"vcpus"`
-	MemoryMb  int32       `json:"memory_mb"`
-	SizeBytes int64       `json:"size_bytes"`
-	TeamID    pgtype.UUID `json:"team_id"`
+	ID          pgtype.UUID `json:"id"`
+	Name        string      `json:"name"`
+	Type        string      `json:"type"`
+	Vcpus       int32       `json:"vcpus"`
+	MemoryMb    int32       `json:"memory_mb"`
+	SizeBytes   int64       `json:"size_bytes"`
+	TeamID      pgtype.UUID `json:"team_id"`
+	DefaultUser string      `json:"default_user"`
+	DefaultEnv  []byte      `json:"default_env"`
 }
 
 func (q *Queries) InsertTemplate(ctx context.Context, arg InsertTemplateParams) (Template, error) {
@@ -162,6 +172,8 @@ func (q *Queries) InsertTemplate(ctx context.Context, arg InsertTemplateParams)
 		arg.MemoryMb,
 		arg.SizeBytes,
 		arg.TeamID,
+		arg.DefaultUser,
+		arg.DefaultEnv,
 	)
 	var i Template
 	err := row.Scan(
@@ -173,12 +185,14 @@ func (q *Queries) InsertTemplate(ctx context.Context, arg InsertTemplateParams)
 		&i.CreatedAt,
 		&i.TeamID,
 		&i.ID,
+		&i.DefaultUser,
+		&i.DefaultEnv,
 	)
 	return i, err
 }
 
 const listTemplates = `-- name: ListTemplates :many
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates ORDER BY created_at DESC
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates ORDER BY created_at DESC
 `
 
 func (q *Queries) ListTemplates(ctx context.Context) ([]Template, error) {
@@ -199,6 +213,8 @@ func (q *Queries) ListTemplates(ctx context.Context) ([]Template, error) {
 			&i.CreatedAt,
 			&i.TeamID,
 			&i.ID,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
@@ -211,7 +227,7 @@ func (q *Queries) ListTemplates(ctx context.Context) ([]Template, error) {
 }
 
 const listTemplatesByTeam = `-- name: ListTemplatesByTeam :many
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-0000-000000000000') ORDER BY created_at DESC
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-0000-000000000000') ORDER BY created_at DESC
 `
 
 // Platform templates are visible to all teams.
@@ -233,6 +249,8 @@ func (q *Queries) ListTemplatesByTeam(ctx context.Context, teamID pgtype.UUID) (
 			&i.CreatedAt,
 			&i.TeamID,
 			&i.ID,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
@@ -245,7 +263,7 @@ func (q *Queries) ListTemplatesByTeam(ctx context.Context, teamID pgtype.UUID) (
 }
 
 const listTemplatesByTeamAndType = `-- name: ListTemplatesByTeamAndType :many
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-0000-000000000000') AND type = $2 ORDER BY created_at DESC
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-0000-000000000000') AND type = $2 ORDER BY created_at DESC
 `
 
 type ListTemplatesByTeamAndTypeParams struct {
@@ -272,6 +290,8 @@ func (q *Queries) ListTemplatesByTeamAndType(ctx context.Context, arg ListTempla
 			&i.CreatedAt,
 			&i.TeamID,
 			&i.ID,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
@@ -284,7 +304,7 @@ func (q *Queries) ListTemplatesByTeamAndType(ctx context.Context, arg ListTempla
 }
 
 const listTemplatesByTeamOnly = `-- name: ListTemplatesByTeamOnly :many
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE team_id = $1 ORDER BY created_at DESC
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE team_id = $1 ORDER BY created_at DESC
 `
 
 // List templates owned by a specific team (NOT including platform templates).
@@ -306,6 +326,8 @@ func (q *Queries) ListTemplatesByTeamOnly(ctx context.Context, teamID pgtype.UUI
 			&i.CreatedAt,
 			&i.TeamID,
 			&i.ID,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
@@ -318,7 +340,7 @@ func (q *Queries) ListTemplatesByTeamOnly(ctx context.Context, teamID pgtype.UUI
 }
 
 const listTemplatesByType = `-- name: ListTemplatesByType :many
-SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id FROM templates WHERE type = $1 ORDER BY created_at DESC
+SELECT name, type, vcpus, memory_mb, size_bytes, created_at, team_id, id, default_user, default_env FROM templates WHERE type = $1 ORDER BY created_at DESC
 `
 
 func (q *Queries) ListTemplatesByType(ctx context.Context, type_ string) ([]Template, error) {
@@ -339,6 +361,8 @@ func (q *Queries) ListTemplatesByType(ctx context.Context, type_ string) ([]Temp
 			&i.CreatedAt,
 			&i.TeamID,
 			&i.ID,
+			&i.DefaultUser,
+			&i.DefaultEnv,
 		); err != nil {
 			return nil, err
 		}
diff --git a/internal/envdclient/client.go b/internal/envdclient/client.go
index 0567cf1..278050e 100644
--- a/internal/envdclient/client.go
+++ b/internal/envdclient/client.go
@@ -3,6 +3,7 @@ package envdclient
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"log/slog"
@@ -273,10 +274,36 @@ func (c *Client) ReadFile(ctx context.Context, path string) ([]byte, error) {
 // env vars and the corresponding files under /run/wrenn/ inside the guest.
 // Must be called after snapshot restore so envd picks up the new sandbox's metadata.
 func (c *Client) PostInit(ctx context.Context) error {
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.base+"/init", nil)
+	return c.PostInitWithDefaults(ctx, "", nil)
+}
+
+// PostInitWithDefaults calls envd's POST /init endpoint with optional default
+// user and environment variables. These are applied to envd's defaults so all
+// subsequent process executions use them.
+func (c *Client) PostInitWithDefaults(ctx context.Context, defaultUser string, envVars map[string]string) error {
+	var body io.Reader
+	if defaultUser != "" || len(envVars) > 0 {
+		payload := make(map[string]any)
+		if defaultUser != "" {
+			payload["defaultUser"] = defaultUser
+		}
+		if len(envVars) > 0 {
+			payload["envVars"] = envVars
+		}
+		data, err := json.Marshal(payload)
+		if err != nil {
+			return fmt.Errorf("marshal init body: %w", err)
+		}
+		body = bytes.NewReader(data)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.base+"/init", body)
 	if err != nil {
 		return fmt.Errorf("create request: %w", err)
 	}
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
 
 	resp, err := c.httpClient.Do(req)
 	if err != nil {
@@ -285,8 +312,8 @@ func (c *Client) PostInit(ctx context.Context) error {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusNoContent {
-		body, _ := io.ReadAll(resp.Body)
-		return fmt.Errorf("post init: status %d: %s", resp.StatusCode, string(body))
+		respBody, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("post init: status %d: %s", resp.StatusCode, string(respBody))
 	}
 
 	return nil
diff --git a/internal/hostagent/server.go b/internal/hostagent/server.go
index fad0d40..7c1315e 100644
--- a/internal/hostagent/server.go
+++ b/internal/hostagent/server.go
@@ -69,6 +69,13 @@ func (s *Server) CreateSandbox(
 		return nil, connect.NewError(connect.CodeInternal, fmt.Errorf("create sandbox: %w", err))
 	}
 
+	// Apply template defaults (user, env vars) if provided.
+	if msg.DefaultUser != "" || len(msg.DefaultEnv) > 0 {
+		if err := s.mgr.SetDefaults(ctx, sb.ID, msg.DefaultUser, msg.DefaultEnv); err != nil {
+			slog.Warn("failed to set sandbox defaults", "sandbox", sb.ID, "error", err)
+		}
+	}
+
 	return connect.NewResponse(&pb.CreateSandboxResponse{
 		SandboxId: sb.ID,
 		Status:    string(sb.Status),
@@ -100,10 +107,19 @@ func (s *Server) ResumeSandbox(
 	ctx context.Context,
 	req *connect.Request[pb.ResumeSandboxRequest],
 ) (*connect.Response[pb.ResumeSandboxResponse], error) {
-	sb, err := s.mgr.Resume(ctx, req.Msg.SandboxId, int(req.Msg.TimeoutSec))
+	msg := req.Msg
+	sb, err := s.mgr.Resume(ctx, msg.SandboxId, int(msg.TimeoutSec))
 	if err != nil {
 		return nil, connect.NewError(connect.CodeInternal, err)
 	}
+
+	// Apply template defaults (user, env vars) if provided.
+	if msg.DefaultUser != "" || len(msg.DefaultEnv) > 0 {
+		if err := s.mgr.SetDefaults(ctx, sb.ID, msg.DefaultUser, msg.DefaultEnv); err != nil {
+			slog.Warn("failed to set sandbox defaults on resume", "sandbox", sb.ID, "error", err)
+		}
+	}
+
 	return connect.NewResponse(&pb.ResumeSandboxResponse{
 		SandboxId: sb.ID,
 		Status:    string(sb.Status),
diff --git a/internal/recipe/context.go b/internal/recipe/context.go
index 71cc0bc..820e717 100644
--- a/internal/recipe/context.go
+++ b/internal/recipe/context.go
@@ -7,10 +7,11 @@ import (
 )
 
 // ExecContext holds mutable state that persists across recipe steps.
-// It is initialized empty and updated by ENV and WORKDIR steps.
+// It is initialized empty and updated by ENV, WORKDIR, and USER steps.
 type ExecContext struct {
 	WorkDir string
 	EnvVars map[string]string
+	User    string // Current unix user for command execution.
 }
 
 // This regex matches:
@@ -25,7 +26,20 @@ var envRegex = regexp.MustCompile(`\$\$|\$\{([a-zA-Z0-9_]*)\}|\$([a-zA-Z0-9_]+)`
 // If WORKDIR and/or ENV are set, they are prepended as a shell preamble:
 //
 //	cd '/the/dir' && KEY='val' /bin/sh -c 'original command'
+//
+// If USER is set to a non-root user, the entire command is wrapped with su:
+//
+//	su <user> -s /bin/sh -c '<preamble + command>'
 func (c *ExecContext) WrappedCommand(cmd string) string {
+	inner := c.innerCommand(cmd)
+	if c.User != "" && c.User != "root" {
+		return "su " + shellescape(c.User) + " -s /bin/sh -c " + shellescape(inner)
+	}
+	return inner
+}
+
+// innerCommand builds the command with workdir/env preamble but without user wrapping.
+func (c *ExecContext) innerCommand(cmd string) string {
 	prefix := c.shellPrefix()
 	if prefix == "" {
 		return cmd
@@ -42,7 +56,11 @@ func (c *ExecContext) WrappedCommand(cmd string) string {
 // simultaneously before a healthcheck is evaluated.
 func (c *ExecContext) StartCommand(cmd string) string {
 	prefix := c.shellPrefix()
-	return prefix + "nohup /bin/sh -c " + shellescape(cmd) + " >/dev/null 2>&1 &"
+	inner := prefix + "nohup /bin/sh -c " + shellescape(cmd) + " >/dev/null 2>&1 &"
+	if c.User != "" && c.User != "root" {
+		return "su " + shellescape(c.User) + " -s /bin/sh -c " + shellescape(inner)
+	}
+	return inner
 }
 
 // shellPrefix builds the "cd ... && KEY=val " preamble for a shell command.
diff --git a/internal/recipe/executor.go b/internal/recipe/executor.go
index 53aaeeb..68c35f9 100644
--- a/internal/recipe/executor.go
+++ b/internal/recipe/executor.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"path"
 	"strings"
 	"time"
 
@@ -16,6 +17,10 @@ import (
 // explicit --timeout flag.
 const DefaultStepTimeout = 30 * time.Second
 
+// BuildFilesDir is the directory inside the sandbox where uploaded build
+// archives are extracted. COPY instructions reference paths relative to this.
+const BuildFilesDir = "/tmp/build-files"
+
 // BuildLogEntry is the per-step record stored in template_builds.logs (JSONB).
 type BuildLogEntry struct {
 	Step    int    `json:"step"`
@@ -32,13 +37,18 @@ type BuildLogEntry struct {
 // the method on the hostagent Connect RPC client.
 type ExecFunc func(ctx context.Context, req *connect.Request[pb.ExecRequest]) (*connect.Response[pb.ExecResponse], error)
 
+// ProgressFunc is called after each step with the current step counter and
+// accumulated log entries. Used for per-step DB progress updates.
+type ProgressFunc func(step int, entries []BuildLogEntry)
+
 // Execute runs steps sequentially against sandboxID using execFn.
 //
 //   - phase labels the log entries (e.g., "pre-build", "recipe", "post-build").
 //   - startStep is the 1-based offset so entries are globally numbered across phases.
 //   - defaultTimeout applies to RUN steps with no per-step --timeout; 0 → 10 minutes.
-//   - bctx is mutated in place as ENV/WORKDIR steps execute, and carries forward
+//   - bctx is mutated in place as ENV/WORKDIR/USER steps execute, and carries forward
 //     into subsequent phases when the caller passes the same pointer.
+//   - onProgress is called after each step for live progress updates (may be nil).
 //
 // Returns all log entries appended during this call, the next step counter
 // value, and whether all steps succeeded. On false the last entry contains
@@ -53,6 +63,7 @@ func Execute(
 	defaultTimeout time.Duration,
 	bctx *ExecContext,
 	execFn ExecFunc,
+	onProgress ProgressFunc,
 ) (entries []BuildLogEntry, nextStep int, ok bool) {
 	if defaultTimeout <= 0 {
 		defaultTimeout = 10 * time.Minute
@@ -72,19 +83,30 @@ func Execute(
 			entries = append(entries, BuildLogEntry{Step: step, Phase: phase, Cmd: st.Raw, Ok: true})
 
 		case KindWORKDIR:
+			// Create the directory if it doesn't exist.
+			mkdirEntry := execRawShell(ctx, st.Raw, sandboxID, phase, step, 10*time.Second, execFn,
+				"mkdir -p "+shellescape(st.Path))
+			if !mkdirEntry.Ok {
+				entries = append(entries, mkdirEntry)
+				return entries, step, false
+			}
 			bctx.WorkDir = st.Path
-			entries = append(entries, BuildLogEntry{Step: step, Phase: phase, Cmd: st.Raw, Ok: true})
+			mkdirEntry.Ok = true
+			entries = append(entries, mkdirEntry)
 
-		case KindUSER, KindCOPY:
-			verb := strings.ToUpper(strings.Fields(st.Raw)[0])
-			entries = append(entries, BuildLogEntry{
-				Step:   step,
-				Phase:  phase,
-				Cmd:    st.Raw,
-				Stderr: verb + " is not yet supported",
-				Ok:     false,
-			})
-			return entries, step, false
+		case KindUSER:
+			entry, succeeded := execUser(ctx, st, sandboxID, phase, step, bctx, execFn)
+			entries = append(entries, entry)
+			if !succeeded {
+				return entries, step, false
+			}
+
+		case KindCOPY:
+			entry, succeeded := execCopy(ctx, st, sandboxID, phase, step, bctx, execFn)
+			entries = append(entries, entry)
+			if !succeeded {
+				return entries, step, false
+			}
 
 		case KindSTART:
 			entry, succeeded := execStart(ctx, st, sandboxID, phase, step, bctx, execFn)
@@ -104,6 +126,10 @@ func Execute(
 				return entries, step, false
 			}
 		}
+
+		if onProgress != nil {
+			onProgress(step, entries)
+		}
 	}
 	return entries, step, true
 }
@@ -145,6 +171,106 @@ func execRun(
 	return entry, entry.Ok
 }
 
+// execUser creates a unix user (if not exists), grants passwordless sudo,
+// and updates bctx.User for subsequent steps.
+func execUser(
+	ctx context.Context,
+	st Step,
+	sandboxID, phase string,
+	step int,
+	bctx *ExecContext,
+	execFn ExecFunc,
+) (BuildLogEntry, bool) {
+	username := st.Key
+	// Create user if not exists, with home directory and bash shell.
+	// Grant passwordless sudo access (E2B convention).
+	// Uses printf %s to avoid shell injection in the sudoers line.
+	script := fmt.Sprintf(
+		"id %s >/dev/null 2>&1 || (adduser --disabled-password --gecos '' --shell /bin/bash %s && printf '%%s ALL=(ALL) NOPASSWD:ALL\\n' %s >> /etc/sudoers)",
+		shellescape(username), shellescape(username), shellescape(username),
+	)
+
+	entry := execRawShell(ctx, st.Raw, sandboxID, phase, step, 30*time.Second, execFn, script)
+	if entry.Ok {
+		bctx.User = username
+	}
+	return entry, entry.Ok
+}
+
+// execCopy copies a file or directory from the build archive (extracted at
+// BuildFilesDir) to the destination path inside the sandbox. Ownership is
+// set to the current user from bctx.
+func execCopy(
+	ctx context.Context,
+	st Step,
+	sandboxID, phase string,
+	step int,
+	bctx *ExecContext,
+	execFn ExecFunc,
+) (BuildLogEntry, bool) {
+	// Validate source path: must be relative and not escape the archive directory.
+	cleaned := path.Clean(st.Src)
+	if strings.HasPrefix(cleaned, "..") || strings.HasPrefix(cleaned, "/") {
+		return BuildLogEntry{
+			Step:   step,
+			Phase:  phase,
+			Cmd:    st.Raw,
+			Stderr: "COPY source must be a relative path within the archive",
+		}, false
+	}
+	src := BuildFilesDir + "/" + cleaned
+	dst := st.Dst
+	owner := "root"
+	if bctx.User != "" {
+		owner = bctx.User
+	}
+	script := fmt.Sprintf(
+		"cp -r %s %s && chown -R %s:%s %s",
+		shellescape(src), shellescape(dst), shellescape(owner), shellescape(owner), shellescape(dst),
+	)
+
+	entry := execRawShell(ctx, st.Raw, sandboxID, phase, step, 60*time.Second, execFn, script)
+	return entry, entry.Ok
+}
+
+// execRawShell runs a shell command directly (as root) without ExecContext
+// wrapping. Used for internal operations like user creation and file copy.
+func execRawShell(
+	ctx context.Context,
+	raw, sandboxID, phase string,
+	step int,
+	timeout time.Duration,
+	execFn ExecFunc,
+	shellCmd string,
+) BuildLogEntry {
+	execCtx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+
+	start := time.Now()
+	resp, err := execFn(execCtx, connect.NewRequest(&pb.ExecRequest{
+		SandboxId:  sandboxID,
+		Cmd:        "/bin/sh",
+		Args:       []string{"-c", shellCmd},
+		TimeoutSec: int32(timeout.Seconds()),
+	}))
+
+	entry := BuildLogEntry{
+		Step:    step,
+		Phase:   phase,
+		Cmd:     raw,
+		Elapsed: time.Since(start).Milliseconds(),
+	}
+	if err != nil {
+		entry.Stderr = fmt.Sprintf("exec error: %v", err)
+		return entry
+	}
+	entry.Stdout = string(resp.Msg.Stdout)
+	entry.Stderr = string(resp.Msg.Stderr)
+	entry.Exit = resp.Msg.ExitCode
+	entry.Ok = resp.Msg.ExitCode == 0
+	return entry
+}
+
 func execStart(
 	ctx context.Context,
 	st Step,
diff --git a/internal/recipe/step.go b/internal/recipe/step.go
index 7d51036..7553aa1 100644
--- a/internal/recipe/step.go
+++ b/internal/recipe/step.go
@@ -24,9 +24,11 @@ type Step struct {
 	Raw     string        // original string, preserved for logging
 	Shell   string        // KindRUN, KindSTART: the shell command text
 	Timeout time.Duration // KindRUN: 0 means use caller's default
-	Key     string        // KindENV: variable name
+	Key     string        // KindENV: variable name; KindUSER: username
 	Value   string        // KindENV: variable value
 	Path    string        // KindWORKDIR: directory path
+	Src     string        // KindCOPY: source path (relative to build archive)
+	Dst     string        // KindCOPY: destination path inside sandbox
 }
 
 // ParseStep parses a single recipe instruction string into a Step.
@@ -61,9 +63,9 @@ func ParseStep(s string) (Step, error) {
 	case "WORKDIR":
 		return parseWORKDIR(s, rest)
 	case "USER":
-		return Step{Kind: KindUSER, Raw: s}, nil
+		return parseUSER(s, rest)
 	case "COPY":
-		return Step{Kind: KindCOPY, Raw: s}, nil
+		return parseCOPY(s, rest)
 	default:
 		return Step{}, fmt.Errorf("unknown instruction %q (expected RUN, START, ENV, WORKDIR, USER, or COPY)", keyword)
 	}
@@ -127,3 +129,31 @@ func parseWORKDIR(raw, path string) (Step, error) {
 	}
 	return Step{Kind: KindWORKDIR, Raw: raw, Path: path}, nil
 }
+
+func parseUSER(raw, username string) (Step, error) {
+	if username == "" {
+		return Step{}, fmt.Errorf("USER requires a username: %q", raw)
+	}
+	// Validate: alphanumeric, hyphens, underscores only; must start with a letter or underscore.
+	for i, c := range username {
+		if i == 0 && !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_') {
+			return Step{}, fmt.Errorf("USER username must start with a letter or underscore: %q", raw)
+		}
+		if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_' || c == '-') {
+			return Step{}, fmt.Errorf("USER username contains invalid character %q: %q", string(c), raw)
+		}
+	}
+	return Step{Kind: KindUSER, Raw: raw, Key: username}, nil
+}
+
+func parseCOPY(raw, rest string) (Step, error) {
+	if rest == "" {
+		return Step{}, fmt.Errorf("COPY requires <src> <dst>: %q", raw)
+	}
+	src, dst, found := strings.Cut(rest, " ")
+	dst = strings.TrimSpace(dst)
+	if !found || dst == "" {
+		return Step{}, fmt.Errorf("COPY requires <src> <dst>: %q", raw)
+	}
+	return Step{Kind: KindCOPY, Raw: raw, Src: src, Dst: dst}, nil
+}
diff --git a/internal/recipe/step_test.go b/internal/recipe/step_test.go
index 2370bb2..7c0def2 100644
--- a/internal/recipe/step_test.go
+++ b/internal/recipe/step_test.go
@@ -111,16 +111,37 @@ func TestParseStep(t *testing.T) {
 			input:   "WORKDIR",
 			wantErr: true,
 		},
-		// USER and COPY stubs
+		// USER
 		{
-			name:  "USER stub",
+			name:  "USER basic",
 			input: "USER www-data",
-			want:  Step{Kind: KindUSER, Raw: "USER www-data"},
+			want:  Step{Kind: KindUSER, Raw: "USER www-data", Key: "www-data"},
 		},
 		{
-			name:  "COPY stub",
+			name:    "USER empty",
+			input:   "USER",
+			wantErr: true,
+		},
+		{
+			name:    "USER invalid chars",
+			input:   "USER bad user",
+			wantErr: true,
+		},
+		// COPY
+		{
+			name:  "COPY basic",
 			input: "COPY config.yaml /etc/app/config.yaml",
-			want:  Step{Kind: KindCOPY, Raw: "COPY config.yaml /etc/app/config.yaml"},
+			want:  Step{Kind: KindCOPY, Raw: "COPY config.yaml /etc/app/config.yaml", Src: "config.yaml", Dst: "/etc/app/config.yaml"},
+		},
+		{
+			name:    "COPY missing dst",
+			input:   "COPY config.yaml",
+			wantErr: true,
+		},
+		{
+			name:    "COPY empty",
+			input:   "COPY",
+			wantErr: true,
 		},
 		// Unknown keyword
 		{
diff --git a/internal/sandbox/manager.go b/internal/sandbox/manager.go
index 7647730..d85d258 100644
--- a/internal/sandbox/manager.go
+++ b/internal/sandbox/manager.go
@@ -1223,6 +1223,23 @@ func (m *Manager) GetClient(sandboxID string) (*envdclient.Client, error) {
 	return sb.client, nil
 }
 
+// SetDefaults calls envd's PostInit to configure the default user and
+// environment variables for a running sandbox. This is called by the host
+// agent after sandbox creation or resume when the template specifies defaults.
+func (m *Manager) SetDefaults(ctx context.Context, sandboxID, defaultUser string, defaultEnv map[string]string) error {
+	if defaultUser == "" && len(defaultEnv) == 0 {
+		return nil
+	}
+	sb, err := m.get(sandboxID)
+	if err != nil {
+		return err
+	}
+	if sb.Status != models.StatusRunning {
+		return fmt.Errorf("sandbox %s is not running (status: %s)", sandboxID, sb.Status)
+	}
+	return sb.client.PostInitWithDefaults(ctx, defaultUser, defaultEnv)
+}
+
 // PtyAttach starts a new PTY process or reconnects to an existing one.
 // If cmd is non-empty, starts a new process. If empty, reconnects using tag.
 func (m *Manager) PtyAttach(ctx context.Context, sandboxID, tag, cmd string, args []string, cols, rows uint32, envs map[string]string, cwd string) (<-chan envdclient.PtyEvent, error) {
diff --git a/internal/service/build.go b/internal/service/build.go
index b45ba1d..55defe6 100644
--- a/internal/service/build.go
+++ b/internal/service/build.go
@@ -27,8 +27,10 @@ const (
 )
 
 // preBuildCmds run before the user recipe to prepare the build environment.
+// apt update runs as root first, then USER switches to wrenn-user for the recipe.
 var preBuildCmds = []string{
 	"RUN apt update",
+	"USER wrenn-user",
 }
 
 // postBuildCmds run after the user recipe to clean up caches and reduce image size.
@@ -36,6 +38,7 @@ var postBuildCmds = []string{
 	"RUN apt clean",
 	"RUN apt autoremove -y",
 	"RUN rm -rf /var/lib/apt/lists/*",
+	"RUN rm -rf /tmp/build-files /tmp/build-files.*",
 }
 
 // buildAgentClient is the subset of the host agent client used by the build worker.
@@ -43,6 +46,7 @@ type buildAgentClient interface {
 	CreateSandbox(ctx context.Context, req *connect.Request[pb.CreateSandboxRequest]) (*connect.Response[pb.CreateSandboxResponse], error)
 	DestroySandbox(ctx context.Context, req *connect.Request[pb.DestroySandboxRequest]) (*connect.Response[pb.DestroySandboxResponse], error)
 	Exec(ctx context.Context, req *connect.Request[pb.ExecRequest]) (*connect.Response[pb.ExecResponse], error)
+	WriteFile(ctx context.Context, req *connect.Request[pb.WriteFileRequest]) (*connect.Response[pb.WriteFileResponse], error)
 	CreateSnapshot(ctx context.Context, req *connect.Request[pb.CreateSnapshotRequest]) (*connect.Response[pb.CreateSnapshotResponse], error)
 	FlattenRootfs(ctx context.Context, req *connect.Request[pb.FlattenRootfsRequest]) (*connect.Response[pb.FlattenRootfsResponse], error)
 }
@@ -56,6 +60,7 @@ type BuildService struct {
 
 	mu        sync.Mutex
 	cancelMap map[string]context.CancelFunc // buildID → per-build cancel func
+	filesMap  map[string][]byte             // buildID → uploaded archive bytes
 }
 
 // BuildCreateParams holds the parameters for creating a template build.
@@ -67,6 +72,27 @@ type BuildCreateParams struct {
 	VCPUs        int32
 	MemoryMB     int32
 	SkipPrePost  bool
+	Archive      []byte // Optional tar/tar.gz/zip archive for COPY commands.
+	ArchiveName  string // Original filename (used to detect format).
+}
+
+// storeArchive stores uploaded archive bytes keyed by build ID for the worker.
+func (s *BuildService) storeArchive(buildID string, data []byte) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.filesMap == nil {
+		s.filesMap = make(map[string][]byte)
+	}
+	s.filesMap[buildID] = data
+}
+
+// takeArchive retrieves and removes stored archive bytes for a build.
+func (s *BuildService) takeArchive(buildID string) []byte {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	data := s.filesMap[buildID]
+	delete(s.filesMap, buildID)
+	return data
 }
 
 // Create inserts a new build record and enqueues it to Redis.
@@ -117,6 +143,11 @@ func (s *BuildService) Create(ctx context.Context, p BuildCreateParams) (db.Temp
 		return db.TemplateBuild{}, fmt.Errorf("enqueue build: %w", err)
 	}
 
+	// Store archive for the worker if provided.
+	if len(p.Archive) > 0 {
+		s.storeArchive(buildIDStr, p.Archive)
+	}
+
 	return build, nil
 }
 
@@ -303,6 +334,16 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 		HostID:    host.ID,
 	})
 
+	// Upload and extract build archive if provided.
+	archive := s.takeArchive(buildIDStr)
+	if len(archive) > 0 {
+		if err := s.uploadAndExtractArchive(buildCtx, agent, sandboxIDStr, archive, buildIDStr); err != nil {
+			s.destroySandbox(buildCtx, agent, sandboxIDStr)
+			s.failBuild(buildCtx, buildID, fmt.Sprintf("archive upload failed: %v", err))
+			return
+		}
+	}
+
 	// Parse recipe steps. preBuildCmds and postBuildCmds are hardcoded and always
 	// valid; panic on error is appropriate here since it would be a programmer mistake.
 	preBuildSteps, err := recipe.ParseRecipe(preBuildCmds)
@@ -331,10 +372,18 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 			"HOME": "/root",
 		}
 	}
-	bctx := &recipe.ExecContext{EnvVars: envVars}
+	bctx := &recipe.ExecContext{EnvVars: envVars, User: "root"}
+
+	// Per-step progress callback for live UI updates.
+	progressFn := func(currentStep int, allEntries []recipe.BuildLogEntry) {
+		s.updateLogs(buildCtx, buildID, currentStep, allEntries)
+	}
 
 	runPhase := func(phase string, steps []recipe.Step, defaultTimeout time.Duration) bool {
-		newEntries, nextStep, ok := recipe.Execute(buildCtx, phase, steps, sandboxIDStr, step, defaultTimeout, bctx, agent.Exec)
+		newEntries, nextStep, ok := recipe.Execute(buildCtx, phase, steps, sandboxIDStr, step, defaultTimeout, bctx, agent.Exec, func(currentStep int, phaseEntries []recipe.BuildLogEntry) {
+			// Progress callback: combine prior logs with current phase entries.
+			progressFn(currentStep, append(logs, phaseEntries...))
+		})
 		logs = append(logs, newEntries...)
 		step = nextStep
 		s.updateLogs(buildCtx, buildID, step, logs)
@@ -344,24 +393,38 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 			if buildCtx.Err() != nil {
 				return false
 			}
-			last := newEntries[len(newEntries)-1]
-			reason := last.Stderr
-			if reason == "" {
-				reason = fmt.Sprintf("exit code %d", last.Exit)
+			reason := "unknown error"
+			if len(newEntries) > 0 {
+				last := newEntries[len(newEntries)-1]
+				reason = last.Stderr
+				if reason == "" {
+					reason = fmt.Sprintf("exit code %d", last.Exit)
+				}
 			}
 			s.failBuild(buildCtx, buildID, fmt.Sprintf("%s step %d failed: %s", phase, step, reason))
 		}
 		return ok
 	}
 
+	// Phase 1: Pre-build (as root) — creates wrenn-user, updates apt.
 	if !build.SkipPrePost {
 		if !runPhase("pre-build", preBuildSteps, 0) {
 			return
 		}
 	}
+
+	// Phase 2: User recipe — starts as wrenn-user (set by USER in pre-build)
+	// or root if skip_pre_post.
 	if !runPhase("recipe", userRecipeSteps, buildCommandTimeout) {
 		return
 	}
+
+	// Capture the final user and env vars as template defaults.
+	templateDefaultUser := bctx.User
+	templateDefaultEnv := bctx.EnvVars
+
+	// Phase 3: Post-build (as root) — cleanup.
+	bctx.User = "root"
 	if !build.SkipPrePost {
 		if !runPhase("post-build", postBuildSteps, 0) {
 			return
@@ -430,19 +493,34 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 		templateType = "snapshot"
 	}
 
+	// Serialize env vars for DB storage.
+	defaultEnvJSON, err := json.Marshal(templateDefaultEnv)
+	if err != nil {
+		defaultEnvJSON = []byte("{}")
+	}
+
 	if _, err := s.DB.InsertTemplate(buildCtx, db.InsertTemplateParams{
-		ID:        build.TemplateID,
-		Name:      build.Name,
-		Type:      templateType,
-		Vcpus:     build.Vcpus,
-		MemoryMb:  build.MemoryMb,
-		SizeBytes: sizeBytes,
-		TeamID:    id.PlatformTeamID,
+		ID:          build.TemplateID,
+		Name:        build.Name,
+		Type:        templateType,
+		Vcpus:       build.Vcpus,
+		MemoryMb:    build.MemoryMb,
+		SizeBytes:   sizeBytes,
+		TeamID:      id.PlatformTeamID,
+		DefaultUser: templateDefaultUser,
+		DefaultEnv:  defaultEnvJSON,
 	}); err != nil {
 		log.Error("failed to insert template record", "error", err)
 		// Build succeeded on disk, just DB record failed — don't mark as failed.
 	}
 
+	// Record defaults on the build record for inspection.
+	_ = s.DB.UpdateBuildDefaults(buildCtx, db.UpdateBuildDefaultsParams{
+		ID:          buildID,
+		DefaultUser: templateDefaultUser,
+		DefaultEnv:  defaultEnvJSON,
+	})
+
 	// For CreateSnapshot, the sandbox is already destroyed by the snapshot process.
 	// For FlattenRootfs, the sandbox is already destroyed by the flatten process.
 	// No additional destroy needed.
@@ -603,3 +681,61 @@ func parseSandboxEnv(raw string) map[string]string {
 
 	return envVars
 }
+
+// uploadAndExtractArchive writes the archive to the sandbox and extracts it
+// to /tmp/build-files/. Detects format from content (tar.gz, tar, zip).
+func (s *BuildService) uploadAndExtractArchive(
+	ctx context.Context,
+	agent buildAgentClient,
+	sandboxID string,
+	archive []byte,
+	buildID string,
+) error {
+	// Detect archive type from magic bytes.
+	var archivePath, extractCmd string
+	switch {
+	case len(archive) >= 2 && archive[0] == 0x1f && archive[1] == 0x8b:
+		// gzip (tar.gz)
+		archivePath = "/tmp/build-files.tar.gz"
+		extractCmd = "mkdir -p /tmp/build-files && tar xzf /tmp/build-files.tar.gz -C /tmp/build-files"
+	case len(archive) >= 4 && string(archive[:4]) == "PK\x03\x04":
+		// zip
+		archivePath = "/tmp/build-files.zip"
+		extractCmd = "mkdir -p /tmp/build-files && unzip -o /tmp/build-files.zip -d /tmp/build-files"
+	case len(archive) >= 262 && string(archive[257:262]) == "ustar":
+		// tar (ustar magic at offset 257)
+		archivePath = "/tmp/build-files.tar"
+		extractCmd = "mkdir -p /tmp/build-files && tar xf /tmp/build-files.tar -C /tmp/build-files"
+	default:
+		// Fallback: try tar.gz
+		archivePath = "/tmp/build-files.tar.gz"
+		extractCmd = "mkdir -p /tmp/build-files && tar xzf /tmp/build-files.tar.gz -C /tmp/build-files"
+	}
+
+	slog.Info("uploading build archive", "build_id", buildID, "path", archivePath, "size", len(archive))
+
+	// Write archive to VM.
+	if _, err := agent.WriteFile(ctx, connect.NewRequest(&pb.WriteFileRequest{
+		SandboxId: sandboxID,
+		Path:      archivePath,
+		Content:   archive,
+	})); err != nil {
+		return fmt.Errorf("write archive: %w", err)
+	}
+
+	// Extract.
+	resp, err := agent.Exec(ctx, connect.NewRequest(&pb.ExecRequest{
+		SandboxId:  sandboxID,
+		Cmd:        "/bin/sh",
+		Args:       []string{"-c", extractCmd},
+		TimeoutSec: 120,
+	}))
+	if err != nil {
+		return fmt.Errorf("extract archive: %w", err)
+	}
+	if resp.Msg.ExitCode != 0 {
+		return fmt.Errorf("extract archive: exit code %d: %s", resp.Msg.ExitCode, string(resp.Msg.Stderr))
+	}
+
+	return nil
+}
diff --git a/internal/service/sandbox.go b/internal/service/sandbox.go
index 68c9bbf..5ebd4d2 100644
--- a/internal/service/sandbox.go
+++ b/internal/service/sandbox.go
@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"log/slog"
 	"time"
@@ -85,6 +86,8 @@ func (s *SandboxService) Create(ctx context.Context, p SandboxCreateParams) (db.
 	// Resolve template name → (teamID, templateID).
 	templateTeamID := id.PlatformTeamID
 	templateID := id.MinimalTemplateID
+	var templateDefaultUser string
+	var templateDefaultEnv map[string]string
 	if p.Template != "minimal" {
 		tmpl, err := s.DB.GetTemplateByTeam(ctx, db.GetTemplateByTeamParams{Name: p.Template, TeamID: p.TeamID})
 		if err != nil {
@@ -92,6 +95,11 @@ func (s *SandboxService) Create(ctx context.Context, p SandboxCreateParams) (db.
 		}
 		templateTeamID = tmpl.TeamID
 		templateID = tmpl.ID
+		templateDefaultUser = tmpl.DefaultUser
+		// Parse default_env JSONB into a map.
+		if len(tmpl.DefaultEnv) > 0 {
+			_ = json.Unmarshal(tmpl.DefaultEnv, &templateDefaultEnv)
+		}
 		// If the template is a snapshot, use its baked-in vcpus/memory.
 		if tmpl.Type == "snapshot" {
 			p.VCPUs = tmpl.Vcpus
@@ -140,14 +148,16 @@ func (s *SandboxService) Create(ctx context.Context, p SandboxCreateParams) (db.
 	}
 
 	resp, err := agent.CreateSandbox(ctx, connect.NewRequest(&pb.CreateSandboxRequest{
-		SandboxId:  sandboxIDStr,
-		Template:   p.Template,
-		TeamId:     id.UUIDString(templateTeamID),
-		TemplateId: id.UUIDString(templateID),
-		Vcpus:      p.VCPUs,
-		MemoryMb:   p.MemoryMB,
-		TimeoutSec: p.TimeoutSec,
-		DiskSizeMb: p.DiskSizeMB,
+		SandboxId:   sandboxIDStr,
+		Template:    p.Template,
+		TeamId:      id.UUIDString(templateTeamID),
+		TemplateId:  id.UUIDString(templateID),
+		Vcpus:       p.VCPUs,
+		MemoryMb:    p.MemoryMB,
+		TimeoutSec:  p.TimeoutSec,
+		DiskSizeMb:  p.DiskSizeMB,
+		DefaultUser: templateDefaultUser,
+		DefaultEnv:  templateDefaultEnv,
 	}))
 	if err != nil {
 		if _, dbErr := s.DB.UpdateSandboxStatus(ctx, db.UpdateSandboxStatusParams{
@@ -249,9 +259,24 @@ func (s *SandboxService) Resume(ctx context.Context, sandboxID, teamID pgtype.UU
 
 	sandboxIDStr := id.FormatSandboxID(sandboxID)
 
+	// Look up template defaults for resume.
+	var resumeDefaultUser string
+	var resumeDefaultEnv map[string]string
+	if sb.TemplateID.Valid {
+		tmpl, err := s.DB.GetTemplate(ctx, sb.TemplateID)
+		if err == nil {
+			resumeDefaultUser = tmpl.DefaultUser
+			if len(tmpl.DefaultEnv) > 0 {
+				_ = json.Unmarshal(tmpl.DefaultEnv, &resumeDefaultEnv)
+			}
+		}
+	}
+
 	resp, err := agent.ResumeSandbox(ctx, connect.NewRequest(&pb.ResumeSandboxRequest{
-		SandboxId:  sandboxIDStr,
-		TimeoutSec: sb.TimeoutSec,
+		SandboxId:   sandboxIDStr,
+		TimeoutSec:  sb.TimeoutSec,
+		DefaultUser: resumeDefaultUser,
+		DefaultEnv:  resumeDefaultEnv,
 	}))
 	if err != nil {
 		return db.Sandbox{}, fmt.Errorf("agent resume: %w", err)
diff --git a/proto/hostagent/gen/hostagent.pb.go b/proto/hostagent/gen/hostagent.pb.go
index c6800b9..ac864ff 100644
--- a/proto/hostagent/gen/hostagent.pb.go
+++ b/proto/hostagent/gen/hostagent.pb.go
@@ -40,7 +40,11 @@ type CreateSandboxRequest struct {
 	// Team UUID that owns the template (hex string). All-zeros = platform.
 	TeamId string `protobuf:"bytes,7,opt,name=team_id,json=teamId,proto3" json:"team_id,omitempty"`
 	// Template UUID (hex string). Both zeros + team zeros = "minimal" sentinel.
-	TemplateId    string `protobuf:"bytes,8,opt,name=template_id,json=templateId,proto3" json:"template_id,omitempty"`
+	TemplateId string `protobuf:"bytes,8,opt,name=template_id,json=templateId,proto3" json:"template_id,omitempty"`
+	// Default unix user for the sandbox (set in envd via PostInit).
+	DefaultUser string `protobuf:"bytes,9,opt,name=default_user,json=defaultUser,proto3" json:"default_user,omitempty"`
+	// Default environment variables (set in envd via PostInit).
+	DefaultEnv    map[string]string `protobuf:"bytes,10,rep,name=default_env,json=defaultEnv,proto3" json:"default_env,omitempty" protobuf_key:"bytes,1,opt,name=key" protobuf_val:"bytes,2,opt,name=value"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -131,6 +135,20 @@ func (x *CreateSandboxRequest) GetTemplateId() string {
 	return ""
 }
 
+func (x *CreateSandboxRequest) GetDefaultUser() string {
+	if x != nil {
+		return x.DefaultUser
+	}
+	return ""
+}
+
+func (x *CreateSandboxRequest) GetDefaultEnv() map[string]string {
+	if x != nil {
+		return x.DefaultEnv
+	}
+	return nil
+}
+
 type CreateSandboxResponse struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	SandboxId     string                 `protobuf:"bytes,1,opt,name=sandbox_id,json=sandboxId,proto3" json:"sandbox_id,omitempty"`
@@ -356,7 +374,11 @@ type ResumeSandboxRequest struct {
 	SandboxId string                 `protobuf:"bytes,1,opt,name=sandbox_id,json=sandboxId,proto3" json:"sandbox_id,omitempty"`
 	// TTL in seconds restored from the DB so the reaper can auto-pause
 	// the sandbox again after inactivity. 0 means no auto-pause.
-	TimeoutSec    int32 `protobuf:"varint,2,opt,name=timeout_sec,json=timeoutSec,proto3" json:"timeout_sec,omitempty"`
+	TimeoutSec int32 `protobuf:"varint,2,opt,name=timeout_sec,json=timeoutSec,proto3" json:"timeout_sec,omitempty"`
+	// Default unix user for the sandbox (set in envd via PostInit on resume).
+	DefaultUser string `protobuf:"bytes,3,opt,name=default_user,json=defaultUser,proto3" json:"default_user,omitempty"`
+	// Default environment variables (set in envd via PostInit on resume).
+	DefaultEnv    map[string]string `protobuf:"bytes,4,rep,name=default_env,json=defaultEnv,proto3" json:"default_env,omitempty" protobuf_key:"bytes,1,opt,name=key" protobuf_val:"bytes,2,opt,name=value"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -405,6 +427,20 @@ func (x *ResumeSandboxRequest) GetTimeoutSec() int32 {
 	return 0
 }
 
+func (x *ResumeSandboxRequest) GetDefaultUser() string {
+	if x != nil {
+		return x.DefaultUser
+	}
+	return ""
+}
+
+func (x *ResumeSandboxRequest) GetDefaultEnv() map[string]string {
+	if x != nil {
+		return x.DefaultEnv
+	}
+	return nil
+}
+
 type ResumeSandboxResponse struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	SandboxId     string                 `protobuf:"bytes,1,opt,name=sandbox_id,json=sandboxId,proto3" json:"sandbox_id,omitempty"`
@@ -3429,7 +3465,7 @@ var File_hostagent_proto protoreflect.FileDescriptor
 
 const file_hostagent_proto_rawDesc = "" +
 	"\n" +
-	"\x0fhostagent.proto\x12\fhostagent.v1\"\x81\x02\n" +
+	"\x0fhostagent.proto\x12\fhostagent.v1\"\xb8\x03\n" +
 	"\x14CreateSandboxRequest\x12\x1d\n" +
 	"\n" +
 	"sandbox_id\x18\x05 \x01(\tR\tsandboxId\x12\x1a\n" +
@@ -3442,7 +3478,14 @@ const file_hostagent_proto_rawDesc = "" +
 	"diskSizeMb\x12\x17\n" +
 	"\ateam_id\x18\a \x01(\tR\x06teamId\x12\x1f\n" +
 	"\vtemplate_id\x18\b \x01(\tR\n" +
-	"templateId\"g\n" +
+	"templateId\x12!\n" +
+	"\fdefault_user\x18\t \x01(\tR\vdefaultUser\x12S\n" +
+	"\vdefault_env\x18\n" +
+	" \x03(\v22.hostagent.v1.CreateSandboxRequest.DefaultEnvEntryR\n" +
+	"defaultEnv\x1a=\n" +
+	"\x0fDefaultEnvEntry\x12\x10\n" +
+	"\x03key\x18\x01 \x01(\tR\x03key\x12\x14\n" +
+	"\x05value\x18\x02 \x01(\tR\x05value:\x028\x01\"g\n" +
 	"\x15CreateSandboxResponse\x12\x1d\n" +
 	"\n" +
 	"sandbox_id\x18\x01 \x01(\tR\tsandboxId\x12\x16\n" +
@@ -3455,12 +3498,18 @@ const file_hostagent_proto_rawDesc = "" +
 	"\x13PauseSandboxRequest\x12\x1d\n" +
 	"\n" +
 	"sandbox_id\x18\x01 \x01(\tR\tsandboxId\"\x16\n" +
-	"\x14PauseSandboxResponse\"V\n" +
+	"\x14PauseSandboxResponse\"\x8d\x02\n" +
 	"\x14ResumeSandboxRequest\x12\x1d\n" +
 	"\n" +
 	"sandbox_id\x18\x01 \x01(\tR\tsandboxId\x12\x1f\n" +
 	"\vtimeout_sec\x18\x02 \x01(\x05R\n" +
-	"timeoutSec\"g\n" +
+	"timeoutSec\x12!\n" +
+	"\fdefault_user\x18\x03 \x01(\tR\vdefaultUser\x12S\n" +
+	"\vdefault_env\x18\x04 \x03(\v22.hostagent.v1.ResumeSandboxRequest.DefaultEnvEntryR\n" +
+	"defaultEnv\x1a=\n" +
+	"\x0fDefaultEnvEntry\x12\x10\n" +
+	"\x03key\x18\x01 \x01(\tR\x03key\x12\x14\n" +
+	"\x05value\x18\x02 \x01(\tR\x05value:\x028\x01\"g\n" +
 	"\x15ResumeSandboxResponse\x12\x1d\n" +
 	"\n" +
 	"sandbox_id\x18\x01 \x01(\tR\tsandboxId\x12\x16\n" +
@@ -3719,7 +3768,7 @@ func file_hostagent_proto_rawDescGZIP() []byte {
 	return file_hostagent_proto_rawDescData
 }
 
-var file_hostagent_proto_msgTypes = make([]protoimpl.MessageInfo, 61)
+var file_hostagent_proto_msgTypes = make([]protoimpl.MessageInfo, 63)
 var file_hostagent_proto_goTypes = []any{
 	(*CreateSandboxRequest)(nil),        // 0: hostagent.v1.CreateSandboxRequest
 	(*CreateSandboxResponse)(nil),       // 1: hostagent.v1.CreateSandboxResponse
@@ -3781,79 +3830,83 @@ var file_hostagent_proto_goTypes = []any{
 	(*PtyResizeResponse)(nil),           // 57: hostagent.v1.PtyResizeResponse
 	(*PtyKillRequest)(nil),              // 58: hostagent.v1.PtyKillRequest
 	(*PtyKillResponse)(nil),             // 59: hostagent.v1.PtyKillResponse
-	nil,                                 // 60: hostagent.v1.PtyAttachRequest.EnvsEntry
+	nil,                                 // 60: hostagent.v1.CreateSandboxRequest.DefaultEnvEntry
+	nil,                                 // 61: hostagent.v1.ResumeSandboxRequest.DefaultEnvEntry
+	nil,                                 // 62: hostagent.v1.PtyAttachRequest.EnvsEntry
 }
 var file_hostagent_proto_depIdxs = []int32{
-	16, // 0: hostagent.v1.ListSandboxesResponse.sandboxes:type_name -> hostagent.v1.SandboxInfo
-	23, // 1: hostagent.v1.ExecStreamResponse.start:type_name -> hostagent.v1.ExecStreamStart
-	24, // 2: hostagent.v1.ExecStreamResponse.data:type_name -> hostagent.v1.ExecStreamData
-	25, // 3: hostagent.v1.ExecStreamResponse.end:type_name -> hostagent.v1.ExecStreamEnd
-	27, // 4: hostagent.v1.WriteFileStreamRequest.meta:type_name -> hostagent.v1.WriteFileStreamMeta
-	33, // 5: hostagent.v1.ListDirResponse.entries:type_name -> hostagent.v1.FileEntry
-	33, // 6: hostagent.v1.MakeDirResponse.entry:type_name -> hostagent.v1.FileEntry
-	42, // 7: hostagent.v1.GetSandboxMetricsResponse.points:type_name -> hostagent.v1.MetricPoint
-	42, // 8: hostagent.v1.FlushSandboxMetricsResponse.points_10m:type_name -> hostagent.v1.MetricPoint
-	42, // 9: hostagent.v1.FlushSandboxMetricsResponse.points_2h:type_name -> hostagent.v1.MetricPoint
-	42, // 10: hostagent.v1.FlushSandboxMetricsResponse.points_24h:type_name -> hostagent.v1.MetricPoint
-	60, // 11: hostagent.v1.PtyAttachRequest.envs:type_name -> hostagent.v1.PtyAttachRequest.EnvsEntry
-	51, // 12: hostagent.v1.PtyAttachResponse.started:type_name -> hostagent.v1.PtyStarted
-	52, // 13: hostagent.v1.PtyAttachResponse.output:type_name -> hostagent.v1.PtyOutput
-	53, // 14: hostagent.v1.PtyAttachResponse.exited:type_name -> hostagent.v1.PtyExited
-	0,  // 15: hostagent.v1.HostAgentService.CreateSandbox:input_type -> hostagent.v1.CreateSandboxRequest
-	2,  // 16: hostagent.v1.HostAgentService.DestroySandbox:input_type -> hostagent.v1.DestroySandboxRequest
-	4,  // 17: hostagent.v1.HostAgentService.PauseSandbox:input_type -> hostagent.v1.PauseSandboxRequest
-	6,  // 18: hostagent.v1.HostAgentService.ResumeSandbox:input_type -> hostagent.v1.ResumeSandboxRequest
-	12, // 19: hostagent.v1.HostAgentService.Exec:input_type -> hostagent.v1.ExecRequest
-	14, // 20: hostagent.v1.HostAgentService.ListSandboxes:input_type -> hostagent.v1.ListSandboxesRequest
-	17, // 21: hostagent.v1.HostAgentService.WriteFile:input_type -> hostagent.v1.WriteFileRequest
-	19, // 22: hostagent.v1.HostAgentService.ReadFile:input_type -> hostagent.v1.ReadFileRequest
-	31, // 23: hostagent.v1.HostAgentService.ListDir:input_type -> hostagent.v1.ListDirRequest
-	34, // 24: hostagent.v1.HostAgentService.MakeDir:input_type -> hostagent.v1.MakeDirRequest
-	36, // 25: hostagent.v1.HostAgentService.RemovePath:input_type -> hostagent.v1.RemovePathRequest
-	8,  // 26: hostagent.v1.HostAgentService.CreateSnapshot:input_type -> hostagent.v1.CreateSnapshotRequest
-	10, // 27: hostagent.v1.HostAgentService.DeleteSnapshot:input_type -> hostagent.v1.DeleteSnapshotRequest
-	21, // 28: hostagent.v1.HostAgentService.ExecStream:input_type -> hostagent.v1.ExecStreamRequest
-	26, // 29: hostagent.v1.HostAgentService.WriteFileStream:input_type -> hostagent.v1.WriteFileStreamRequest
-	29, // 30: hostagent.v1.HostAgentService.ReadFileStream:input_type -> hostagent.v1.ReadFileStreamRequest
-	38, // 31: hostagent.v1.HostAgentService.PingSandbox:input_type -> hostagent.v1.PingSandboxRequest
-	40, // 32: hostagent.v1.HostAgentService.Terminate:input_type -> hostagent.v1.TerminateRequest
-	43, // 33: hostagent.v1.HostAgentService.GetSandboxMetrics:input_type -> hostagent.v1.GetSandboxMetricsRequest
-	45, // 34: hostagent.v1.HostAgentService.FlushSandboxMetrics:input_type -> hostagent.v1.FlushSandboxMetricsRequest
-	47, // 35: hostagent.v1.HostAgentService.FlattenRootfs:input_type -> hostagent.v1.FlattenRootfsRequest
-	49, // 36: hostagent.v1.HostAgentService.PtyAttach:input_type -> hostagent.v1.PtyAttachRequest
-	54, // 37: hostagent.v1.HostAgentService.PtySendInput:input_type -> hostagent.v1.PtySendInputRequest
-	56, // 38: hostagent.v1.HostAgentService.PtyResize:input_type -> hostagent.v1.PtyResizeRequest
-	58, // 39: hostagent.v1.HostAgentService.PtyKill:input_type -> hostagent.v1.PtyKillRequest
-	1,  // 40: hostagent.v1.HostAgentService.CreateSandbox:output_type -> hostagent.v1.CreateSandboxResponse
-	3,  // 41: hostagent.v1.HostAgentService.DestroySandbox:output_type -> hostagent.v1.DestroySandboxResponse
-	5,  // 42: hostagent.v1.HostAgentService.PauseSandbox:output_type -> hostagent.v1.PauseSandboxResponse
-	7,  // 43: hostagent.v1.HostAgentService.ResumeSandbox:output_type -> hostagent.v1.ResumeSandboxResponse
-	13, // 44: hostagent.v1.HostAgentService.Exec:output_type -> hostagent.v1.ExecResponse
-	15, // 45: hostagent.v1.HostAgentService.ListSandboxes:output_type -> hostagent.v1.ListSandboxesResponse
-	18, // 46: hostagent.v1.HostAgentService.WriteFile:output_type -> hostagent.v1.WriteFileResponse
-	20, // 47: hostagent.v1.HostAgentService.ReadFile:output_type -> hostagent.v1.ReadFileResponse
-	32, // 48: hostagent.v1.HostAgentService.ListDir:output_type -> hostagent.v1.ListDirResponse
-	35, // 49: hostagent.v1.HostAgentService.MakeDir:output_type -> hostagent.v1.MakeDirResponse
-	37, // 50: hostagent.v1.HostAgentService.RemovePath:output_type -> hostagent.v1.RemovePathResponse
-	9,  // 51: hostagent.v1.HostAgentService.CreateSnapshot:output_type -> hostagent.v1.CreateSnapshotResponse
-	11, // 52: hostagent.v1.HostAgentService.DeleteSnapshot:output_type -> hostagent.v1.DeleteSnapshotResponse
-	22, // 53: hostagent.v1.HostAgentService.ExecStream:output_type -> hostagent.v1.ExecStreamResponse
-	28, // 54: hostagent.v1.HostAgentService.WriteFileStream:output_type -> hostagent.v1.WriteFileStreamResponse
-	30, // 55: hostagent.v1.HostAgentService.ReadFileStream:output_type -> hostagent.v1.ReadFileStreamResponse
-	39, // 56: hostagent.v1.HostAgentService.PingSandbox:output_type -> hostagent.v1.PingSandboxResponse
-	41, // 57: hostagent.v1.HostAgentService.Terminate:output_type -> hostagent.v1.TerminateResponse
-	44, // 58: hostagent.v1.HostAgentService.GetSandboxMetrics:output_type -> hostagent.v1.GetSandboxMetricsResponse
-	46, // 59: hostagent.v1.HostAgentService.FlushSandboxMetrics:output_type -> hostagent.v1.FlushSandboxMetricsResponse
-	48, // 60: hostagent.v1.HostAgentService.FlattenRootfs:output_type -> hostagent.v1.FlattenRootfsResponse
-	50, // 61: hostagent.v1.HostAgentService.PtyAttach:output_type -> hostagent.v1.PtyAttachResponse
-	55, // 62: hostagent.v1.HostAgentService.PtySendInput:output_type -> hostagent.v1.PtySendInputResponse
-	57, // 63: hostagent.v1.HostAgentService.PtyResize:output_type -> hostagent.v1.PtyResizeResponse
-	59, // 64: hostagent.v1.HostAgentService.PtyKill:output_type -> hostagent.v1.PtyKillResponse
-	40, // [40:65] is the sub-list for method output_type
-	15, // [15:40] is the sub-list for method input_type
-	15, // [15:15] is the sub-list for extension type_name
-	15, // [15:15] is the sub-list for extension extendee
-	0,  // [0:15] is the sub-list for field type_name
+	60, // 0: hostagent.v1.CreateSandboxRequest.default_env:type_name -> hostagent.v1.CreateSandboxRequest.DefaultEnvEntry
+	61, // 1: hostagent.v1.ResumeSandboxRequest.default_env:type_name -> hostagent.v1.ResumeSandboxRequest.DefaultEnvEntry
+	16, // 2: hostagent.v1.ListSandboxesResponse.sandboxes:type_name -> hostagent.v1.SandboxInfo
+	23, // 3: hostagent.v1.ExecStreamResponse.start:type_name -> hostagent.v1.ExecStreamStart
+	24, // 4: hostagent.v1.ExecStreamResponse.data:type_name -> hostagent.v1.ExecStreamData
+	25, // 5: hostagent.v1.ExecStreamResponse.end:type_name -> hostagent.v1.ExecStreamEnd
+	27, // 6: hostagent.v1.WriteFileStreamRequest.meta:type_name -> hostagent.v1.WriteFileStreamMeta
+	33, // 7: hostagent.v1.ListDirResponse.entries:type_name -> hostagent.v1.FileEntry
+	33, // 8: hostagent.v1.MakeDirResponse.entry:type_name -> hostagent.v1.FileEntry
+	42, // 9: hostagent.v1.GetSandboxMetricsResponse.points:type_name -> hostagent.v1.MetricPoint
+	42, // 10: hostagent.v1.FlushSandboxMetricsResponse.points_10m:type_name -> hostagent.v1.MetricPoint
+	42, // 11: hostagent.v1.FlushSandboxMetricsResponse.points_2h:type_name -> hostagent.v1.MetricPoint
+	42, // 12: hostagent.v1.FlushSandboxMetricsResponse.points_24h:type_name -> hostagent.v1.MetricPoint
+	62, // 13: hostagent.v1.PtyAttachRequest.envs:type_name -> hostagent.v1.PtyAttachRequest.EnvsEntry
+	51, // 14: hostagent.v1.PtyAttachResponse.started:type_name -> hostagent.v1.PtyStarted
+	52, // 15: hostagent.v1.PtyAttachResponse.output:type_name -> hostagent.v1.PtyOutput
+	53, // 16: hostagent.v1.PtyAttachResponse.exited:type_name -> hostagent.v1.PtyExited
+	0,  // 17: hostagent.v1.HostAgentService.CreateSandbox:input_type -> hostagent.v1.CreateSandboxRequest
+	2,  // 18: hostagent.v1.HostAgentService.DestroySandbox:input_type -> hostagent.v1.DestroySandboxRequest
+	4,  // 19: hostagent.v1.HostAgentService.PauseSandbox:input_type -> hostagent.v1.PauseSandboxRequest
+	6,  // 20: hostagent.v1.HostAgentService.ResumeSandbox:input_type -> hostagent.v1.ResumeSandboxRequest
+	12, // 21: hostagent.v1.HostAgentService.Exec:input_type -> hostagent.v1.ExecRequest
+	14, // 22: hostagent.v1.HostAgentService.ListSandboxes:input_type -> hostagent.v1.ListSandboxesRequest
+	17, // 23: hostagent.v1.HostAgentService.WriteFile:input_type -> hostagent.v1.WriteFileRequest
+	19, // 24: hostagent.v1.HostAgentService.ReadFile:input_type -> hostagent.v1.ReadFileRequest
+	31, // 25: hostagent.v1.HostAgentService.ListDir:input_type -> hostagent.v1.ListDirRequest
+	34, // 26: hostagent.v1.HostAgentService.MakeDir:input_type -> hostagent.v1.MakeDirRequest
+	36, // 27: hostagent.v1.HostAgentService.RemovePath:input_type -> hostagent.v1.RemovePathRequest
+	8,  // 28: hostagent.v1.HostAgentService.CreateSnapshot:input_type -> hostagent.v1.CreateSnapshotRequest
+	10, // 29: hostagent.v1.HostAgentService.DeleteSnapshot:input_type -> hostagent.v1.DeleteSnapshotRequest
+	21, // 30: hostagent.v1.HostAgentService.ExecStream:input_type -> hostagent.v1.ExecStreamRequest
+	26, // 31: hostagent.v1.HostAgentService.WriteFileStream:input_type -> hostagent.v1.WriteFileStreamRequest
+	29, // 32: hostagent.v1.HostAgentService.ReadFileStream:input_type -> hostagent.v1.ReadFileStreamRequest
+	38, // 33: hostagent.v1.HostAgentService.PingSandbox:input_type -> hostagent.v1.PingSandboxRequest
+	40, // 34: hostagent.v1.HostAgentService.Terminate:input_type -> hostagent.v1.TerminateRequest
+	43, // 35: hostagent.v1.HostAgentService.GetSandboxMetrics:input_type -> hostagent.v1.GetSandboxMetricsRequest
+	45, // 36: hostagent.v1.HostAgentService.FlushSandboxMetrics:input_type -> hostagent.v1.FlushSandboxMetricsRequest
+	47, // 37: hostagent.v1.HostAgentService.FlattenRootfs:input_type -> hostagent.v1.FlattenRootfsRequest
+	49, // 38: hostagent.v1.HostAgentService.PtyAttach:input_type -> hostagent.v1.PtyAttachRequest
+	54, // 39: hostagent.v1.HostAgentService.PtySendInput:input_type -> hostagent.v1.PtySendInputRequest
+	56, // 40: hostagent.v1.HostAgentService.PtyResize:input_type -> hostagent.v1.PtyResizeRequest
+	58, // 41: hostagent.v1.HostAgentService.PtyKill:input_type -> hostagent.v1.PtyKillRequest
+	1,  // 42: hostagent.v1.HostAgentService.CreateSandbox:output_type -> hostagent.v1.CreateSandboxResponse
+	3,  // 43: hostagent.v1.HostAgentService.DestroySandbox:output_type -> hostagent.v1.DestroySandboxResponse
+	5,  // 44: hostagent.v1.HostAgentService.PauseSandbox:output_type -> hostagent.v1.PauseSandboxResponse
+	7,  // 45: hostagent.v1.HostAgentService.ResumeSandbox:output_type -> hostagent.v1.ResumeSandboxResponse
+	13, // 46: hostagent.v1.HostAgentService.Exec:output_type -> hostagent.v1.ExecResponse
+	15, // 47: hostagent.v1.HostAgentService.ListSandboxes:output_type -> hostagent.v1.ListSandboxesResponse
+	18, // 48: hostagent.v1.HostAgentService.WriteFile:output_type -> hostagent.v1.WriteFileResponse
+	20, // 49: hostagent.v1.HostAgentService.ReadFile:output_type -> hostagent.v1.ReadFileResponse
+	32, // 50: hostagent.v1.HostAgentService.ListDir:output_type -> hostagent.v1.ListDirResponse
+	35, // 51: hostagent.v1.HostAgentService.MakeDir:output_type -> hostagent.v1.MakeDirResponse
+	37, // 52: hostagent.v1.HostAgentService.RemovePath:output_type -> hostagent.v1.RemovePathResponse
+	9,  // 53: hostagent.v1.HostAgentService.CreateSnapshot:output_type -> hostagent.v1.CreateSnapshotResponse
+	11, // 54: hostagent.v1.HostAgentService.DeleteSnapshot:output_type -> hostagent.v1.DeleteSnapshotResponse
+	22, // 55: hostagent.v1.HostAgentService.ExecStream:output_type -> hostagent.v1.ExecStreamResponse
+	28, // 56: hostagent.v1.HostAgentService.WriteFileStream:output_type -> hostagent.v1.WriteFileStreamResponse
+	30, // 57: hostagent.v1.HostAgentService.ReadFileStream:output_type -> hostagent.v1.ReadFileStreamResponse
+	39, // 58: hostagent.v1.HostAgentService.PingSandbox:output_type -> hostagent.v1.PingSandboxResponse
+	41, // 59: hostagent.v1.HostAgentService.Terminate:output_type -> hostagent.v1.TerminateResponse
+	44, // 60: hostagent.v1.HostAgentService.GetSandboxMetrics:output_type -> hostagent.v1.GetSandboxMetricsResponse
+	46, // 61: hostagent.v1.HostAgentService.FlushSandboxMetrics:output_type -> hostagent.v1.FlushSandboxMetricsResponse
+	48, // 62: hostagent.v1.HostAgentService.FlattenRootfs:output_type -> hostagent.v1.FlattenRootfsResponse
+	50, // 63: hostagent.v1.HostAgentService.PtyAttach:output_type -> hostagent.v1.PtyAttachResponse
+	55, // 64: hostagent.v1.HostAgentService.PtySendInput:output_type -> hostagent.v1.PtySendInputResponse
+	57, // 65: hostagent.v1.HostAgentService.PtyResize:output_type -> hostagent.v1.PtyResizeResponse
+	59, // 66: hostagent.v1.HostAgentService.PtyKill:output_type -> hostagent.v1.PtyKillResponse
+	42, // [42:67] is the sub-list for method output_type
+	17, // [17:42] is the sub-list for method input_type
+	17, // [17:17] is the sub-list for extension type_name
+	17, // [17:17] is the sub-list for extension extendee
+	0,  // [0:17] is the sub-list for field type_name
 }
 
 func init() { file_hostagent_proto_init() }
@@ -3886,7 +3939,7 @@ func file_hostagent_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_hostagent_proto_rawDesc), len(file_hostagent_proto_rawDesc)),
 			NumEnums:      0,
-			NumMessages:   61,
+			NumMessages:   63,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
diff --git a/proto/hostagent/hostagent.proto b/proto/hostagent/hostagent.proto
index ea6c4eb..6b6306e 100644
--- a/proto/hostagent/hostagent.proto
+++ b/proto/hostagent/hostagent.proto
@@ -119,6 +119,12 @@ message CreateSandboxRequest {
 
   // Template UUID (hex string). Both zeros + team zeros = "minimal" sentinel.
   string template_id = 8;
+
+  // Default unix user for the sandbox (set in envd via PostInit).
+  string default_user = 9;
+
+  // Default environment variables (set in envd via PostInit).
+  map<string, string> default_env = 10;
 }
 
 message CreateSandboxResponse {
@@ -145,6 +151,12 @@ message ResumeSandboxRequest {
   // TTL in seconds restored from the DB so the reaper can auto-pause
   // the sandbox again after inactivity. 0 means no auto-pause.
   int32 timeout_sec = 2;
+
+  // Default unix user for the sandbox (set in envd via PostInit on resume).
+  string default_user = 3;
+
+  // Default environment variables (set in envd via PostInit on resume).
+  map<string, string> default_env = 4;
 }
 
 message ResumeSandboxResponse {