diff --git a/internal/api/handlers_pty.go b/internal/api/handlers_pty.go
index 6a906b1..cd5dcae 100644
--- a/internal/api/handlers_pty.go
+++ b/internal/api/handlers_pty.go
@@ -23,7 +23,6 @@ import (
 )
 
 const (
-	ptyInactivityTimeout = 120 * time.Second
 	ptyKeepaliveInterval = 30 * time.Second
 	ptyDefaultCmd        = "/bin/bash"
 	ptyDefaultCols       = 80
@@ -246,10 +245,6 @@ func runPtyLoop(
 ) {
 	var wg sync.WaitGroup
 
-	// Inactivity timer — reset on input/resize, fires kill after timeout.
-	timer := time.NewTimer(ptyInactivityTimeout)
-	defer timer.Stop()
-
 	// Output pump: read from Connect stream, write to WebSocket.
 	wg.Add(1)
 	go func() {
@@ -317,7 +312,6 @@ func runPtyLoop(
 				})); err != nil {
 					slog.Debug("pty send input error", "error", err)
 				}
-				resetTimer(timer, ptyInactivityTimeout)
 
 			case "resize":
 				cols := msg.Cols
@@ -331,7 +325,6 @@ func runPtyLoop(
 					})); err != nil {
 						slog.Debug("pty resize error", "error", err)
 					}
-					resetTimer(timer, ptyInactivityTimeout)
 				}
 
 			case "kill":
@@ -364,26 +357,6 @@ func runPtyLoop(
 		}
 	}()
 
-	// Inactivity timeout goroutine.
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
-		select {
-		case <-timer.C:
-			slog.Info("pty session timed out", "sandbox_id", sandboxID, "tag", tag)
-			rpcCtx, rpcCancel := context.WithTimeout(context.Background(), 5*time.Second)
-			if _, err := agent.PtyKill(rpcCtx, connect.NewRequest(&pb.PtyKillRequest{
-				SandboxId: sandboxID,
-				Tag:       tag,
-			})); err != nil {
-				slog.Debug("pty timeout kill error", "error", err)
-			}
-			rpcCancel()
-			cancel()
-		case <-ctx.Done():
-		}
-	}()
-
 	wg.Wait()
 }
 
@@ -391,15 +364,3 @@ func runPtyLoop(
 func newPtyTag() string {
 	return "pty-" + id.NewPtyTag()
 }
-
-// resetTimer safely resets a timer by stopping it and draining the channel
-// before resetting, avoiding the race documented in time.Timer.Reset.
-func resetTimer(t *time.Timer, d time.Duration) {
-	if !t.Stop() {
-		select {
-		case <-t.C:
-		default:
-		}
-	}
-	t.Reset(d)
-}
diff --git a/internal/api/openapi.yaml b/internal/api/openapi.yaml
index 031cefd..984a37d 100644
--- a/internal/api/openapi.yaml
+++ b/internal/api/openapi.yaml
@@ -1386,7 +1386,6 @@ paths:
         PTY data (input and output) is base64-encoded because it contains raw
         terminal bytes (escape sequences, control codes) that are not valid UTF-8.
 
-        Sessions have a 120-second inactivity timeout (reset on input/resize).
         Sessions persist across WebSocket disconnections — the process keeps
         running in the capsule. Use the `tag` from the "started" response to
         reconnect later.
diff --git a/internal/recipe/context.go b/internal/recipe/context.go
index 820e717..3a64059 100644
--- a/internal/recipe/context.go
+++ b/internal/recipe/context.go
@@ -115,8 +115,11 @@ func expandEnv(s string, vars map[string]string) string {
 	})
 }
 
-// shellescape wraps s in single quotes, escaping any embedded single quotes.
+// Shellescape wraps s in single quotes, escaping any embedded single quotes.
 // This is POSIX-safe for paths, env values, and shell commands.
-func shellescape(s string) string {
+func Shellescape(s string) string {
 	return "'" + strings.ReplaceAll(s, "'", `'\''`) + "'"
 }
+
+// shellescape is the package-internal alias for Shellescape.
+func shellescape(s string) string { return Shellescape(s) }
diff --git a/internal/recipe/executor.go b/internal/recipe/executor.go
index 38a8b12..ffecf04 100644
--- a/internal/recipe/executor.go
+++ b/internal/recipe/executor.go
@@ -193,6 +193,15 @@ func execUser(
 	entry := execRawShell(ctx, st.Raw, sandboxID, phase, step, 30*time.Second, execFn, script)
 	if entry.Ok {
 		bctx.User = username
+		// Update HOME so ~ expands correctly in subsequent RUN/WORKDIR steps.
+		if bctx.EnvVars == nil {
+			bctx.EnvVars = make(map[string]string)
+		}
+		if username == "root" {
+			bctx.EnvVars["HOME"] = "/root"
+		} else {
+			bctx.EnvVars["HOME"] = "/home/" + username
+		}
 	}
 	return entry, entry.Ok
 }
diff --git a/internal/sandbox/manager.go b/internal/sandbox/manager.go
index 3dde053..576a3e9 100644
--- a/internal/sandbox/manager.go
+++ b/internal/sandbox/manager.go
@@ -901,6 +901,18 @@ func (m *Manager) FlattenRootfs(ctx context.Context, sandboxID string, teamID, t
 		return 0, fmt.Errorf("sandbox %s not found", sandboxID)
 	}
 
+	// Flush guest page cache to disk before stopping the VM. Without this,
+	// files written by the build (e.g. pip-installed packages) may exist in the
+	// guest's page cache but not yet on the dm block device — flatten would then
+	// capture 0-byte files.
+	func() {
+		syncCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
+		defer cancel()
+		if _, err := sb.client.Exec(syncCtx, "/bin/sync"); err != nil {
+			slog.Warn("flatten: guest sync failed (non-fatal)", "id", sb.ID, "error", err)
+		}
+	}()
+
 	// Stop the VM but keep the dm device alive for flattening.
 	m.stopSampler(sb)
 	if err := m.vm.Destroy(ctx, sb.ID); err != nil {
diff --git a/internal/service/build.go b/internal/service/build.go
index 563c8cd..92d826d 100644
--- a/internal/service/build.go
+++ b/internal/service/build.go
@@ -444,7 +444,7 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 			return
 		}
 		log.Info("running healthcheck", "cmd", hc.Cmd, "interval", hc.Interval, "timeout", hc.Timeout, "start_period", hc.StartPeriod, "retries", hc.Retries)
-		if err := s.waitForHealthcheck(buildCtx, agent, sandboxIDStr, hc); err != nil {
+		if err := s.waitForHealthcheck(buildCtx, agent, sandboxIDStr, hc, templateDefaultUser); err != nil {
 			s.destroySandbox(buildCtx, agent, sandboxIDStr)
 			if buildCtx.Err() != nil {
 				return
@@ -544,7 +544,14 @@ func (s *BuildService) executeBuild(ctx context.Context, buildIDStr string) {
 // During the start period, failures are not counted toward the retry budget.
 // Returns nil on the first successful check, or an error if retries are
 // exhausted, the deadline passes, or the context is cancelled.
-func (s *BuildService) waitForHealthcheck(ctx context.Context, agent buildAgentClient, sandboxIDStr string, hc recipe.HealthcheckConfig) error {
+func (s *BuildService) waitForHealthcheck(ctx context.Context, agent buildAgentClient, sandboxIDStr string, hc recipe.HealthcheckConfig, user string) error {
+	// Wrap the healthcheck command with su when a non-root user is set, so that
+	// ~ expands to the correct home directory and the process runs with the
+	// right UID (matching the template's default user).
+	cmd := hc.Cmd
+	if user != "" && user != "root" {
+		cmd = "su " + recipe.Shellescape(user) + " -s /bin/sh -c " + recipe.Shellescape(hc.Cmd)
+	}
 	ticker := time.NewTicker(hc.Interval)
 	defer ticker.Stop()
 
@@ -571,7 +578,7 @@ func (s *BuildService) waitForHealthcheck(ctx context.Context, agent buildAgentC
 			resp, err := agent.Exec(execCtx, connect.NewRequest(&pb.ExecRequest{
 				SandboxId:  sandboxIDStr,
 				Cmd:        "/bin/sh",
-				Args:       []string{"-c", hc.Cmd},
+				Args:       []string{"-c", cmd},
 				TimeoutSec: int32(hc.Timeout.Seconds()),
 			}))
 			cancel()
diff --git a/recipes/code-runner-beta.healthcheck b/recipes/code-runner-beta.healthcheck
new file mode 100644
index 0000000..186da39
--- /dev/null
+++ b/recipes/code-runner-beta.healthcheck
@@ -0,0 +1 @@
+--interval=5s --timeout=5s --start-period=60s --retries=5 curl -sf http://127.0.0.1:8888/api/status
diff --git a/recipes/code-runner-beta.recipefile b/recipes/code-runner-beta.recipefile
new file mode 100644
index 0000000..dc96779
--- /dev/null
+++ b/recipes/code-runner-beta.recipefile
@@ -0,0 +1,9 @@
+RUN --timeout=5m sudo apt install -y python3 python3-pip python3-venv
+ENV PYTHONUNBUFFERED=1
+
+RUN python3 -m venv ~/jupyter-env
+RUN --timeout=5m ~/jupyter-env/bin/pip install --upgrade pip
+RUN --timeout=5m ~/jupyter-env/bin/pip install jupyter-server ipykernel
+RUN --timeout=5m ~/jupyter-env/bin/python -m ipykernel install --sys-prefix
+
+START ~/jupyter-env/bin/jupyter server --ServerApp.ip=0.0.0.0 --ServerApp.port=8888 --ServerApp.token='' --ServerApp.password='' --ServerApp.allow_origin='*' --ServerApp.disable_check_xsrf=True --no-browser --log-level=INFO
diff --git a/recipes/python-interpreter-v0-beta.healthcheck b/recipes/python-interpreter-v0-beta.healthcheck
deleted file mode 100644
index ca2555c..0000000
--- a/recipes/python-interpreter-v0-beta.healthcheck
+++ /dev/null
@@ -1 +0,0 @@
---interval=5s --timeout=3s --start-period=3s --retries=3 python3 -c "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8888/api/status', timeout=3)"
diff --git a/recipes/python-interpreter-v0-beta.recipefile b/recipes/python-interpreter-v0-beta.recipefile
deleted file mode 100644
index e83f5da..0000000
--- a/recipes/python-interpreter-v0-beta.recipefile
+++ /dev/null
@@ -1,7 +0,0 @@
-RUN apt-get install -y --no-install-recommends python3 python3-pip python3-venv
-RUN python3 -m venv /opt/venv
-ENV PATH=/opt/venv/bin:$PATH
-
-RUN --timeout=5m pip install --no-cache-dir jupyter-server ipykernel
-
-START jupyter server --ServerApp.ip=0.0.0.0 --ServerApp.port=8888 --ServerApp.token='' --ServerApp.allow_origin='*' --ServerApp.disable_check_xsrf=True --no-browser --allow-root