diff --git a/docs/dev/ADR-001-branchless-worktree-architecture.md b/docs/dev/ADR-001-branchless-worktree-architecture.md
index c9d90193f..34cdf2dfd 100644
--- a/docs/dev/ADR-001-branchless-worktree-architecture.md
+++ b/docs/dev/ADR-001-branchless-worktree-architecture.md
@@ -1,7 +1,8 @@
 # ADR-001: Branchless Worktree Architecture
 
-**Status:** Accepted
+**Status:** Accepted — partial drift
 **Date:** 2026-03-15
+**Revised:** 2026-05-02 — partial drift documented; code migration incomplete
 **Deciders:** Lex Christopherson
 **Advisors:** Claude Opus 4.6, Gemini 2.5 Pro, GPT-5.4 (Codex)
 
@@ -147,12 +148,14 @@ Planning artifacts (milestones/, PROJECT.md, DECISIONS.md, REQUIREMENTS.md, QUEU
 |------|--------------|----------------|
 | `auto-worktree.ts` | ~246 | `mergeSliceToMilestone()`, `shouldUseWorktreeIsolation()`, `getMergeToMainMode()`, slice merge guards |
 | `git-service.ts` | ~250 | `mergeSliceToMain()`, conflict resolution, runtime stripping post-merge, `ensureSliceBranch()`, `switchToMain()` |
-| `git-self-heal.ts` | ~86 | `abortAndReset()`, `withMergeHeal()` (merge-specific recovery) |
-| `auto.ts` | ~150 | Merge dispatch guards, `fix-merge` dispatch path, branch-mode routing |
-| `worktree.ts` | ~40 | `getSliceBranchName()`, `ensureSliceBranch()`, `mergeSliceToMain()` delegates |
+| `git-self-heal.ts` | ~86 | `abortAndReset()`, `withMergeHeal()` (merge-specific recovery) **(still present — see Drift section)** |
+| `auto.ts` | ~150 | Merge dispatch guards, `fix-merge` dispatch path, branch-mode routing **(partially still present — see Drift section)** |
+| `worktree.ts` | ~40 | `getSliceBranchName()`, `ensureSliceBranch()`, `mergeSliceToMain()` delegates **(getSliceBranchName still present — see Drift section)** |
 | **Test files** | ~11 files | `auto-worktree-merge.test.ts`, `auto-worktree-milestone-merge.test.ts`, merge-related test cases |
 | **Total** | **~770+ lines** | |
 
+*Verified 2026-05-02: mergeSliceToMilestone and the original mergeSliceToMain (git-service.ts) are deleted. Several other items listed above are still present — see Drift section below. Current authoritative milestone merge path: `src/resources/extensions/sf/auto-worktree.ts:1616` (`mergeMilestoneToMain`). A separate newer function `mergeSliceToMain` at `src/resources/extensions/sf/slice-cadence.ts:92` was added post-ADR for the slice-cadence collapse feature (#4765) and is unrelated to the deleted branch-era function.*
+
 ### What `mergeMilestoneToMain()` Becomes
 
 The function simplifies dramatically:
@@ -174,6 +177,8 @@ The force-add of `SF_DURABLE_PATHS` is no longer needed — planning artifacts a
 
 The `_runtimeFilesCleanedUp` one-time migration logic can also be removed.
 
+*Verified 2026-05-02: `smartStage()` at `src/resources/extensions/sf/git-service.ts:576` is still present in its original form, including `_runtimeFilesCleanedUp` migration logic and `SF_MILESTONE_LOCK` parallel-scope logic. The simplification described here has not been performed — see Drift section.*
+
 ### What Happens to `handleAgentEnd()`
 
 After any unit completes:
@@ -188,6 +193,8 @@ The "Path A fix" (lines 937-953) becomes the only path. No branch mismatch possi
 
 The `fix-merge` dispatch unit type is eliminated. Within a worktree, there are no merges that can conflict. The only merge is milestone→main (squash), and if that conflicts (rare, parallel milestone edge case), it's handled as a one-time resolution at milestone completion — not a dispatch loop.
 
+*Verified 2026-05-02: The `fix-merge` prompt template has been deleted (no `fix-merge.md` exists in `src/resources/extensions/sf/prompts/`). However, `MergeConflictError` (re-exported from `git-service.ts:201`) is still present along with a JSDoc comment at `git-service.ts:199` that still mentions dispatching a "fix-merge session". No active dispatch-loop code was found — this appears to be residual documentation in the class definition, not active dispatch logic. Treated as "still present (partial)" in the Drift section.*
+
 ### Backwards Compatibility
 
 The `shouldUseWorktreeIsolation()` three-tier preference resolution is replaced by a single behavior: worktree isolation is always used. The `git.isolation: "branch"` preference is deprecated.
@@ -277,3 +284,28 @@ Response: Accepted in spirit. Commits with conventional tags (`feat(M001/S01):`,
    - Update/delete 11 test files
    - Update README suggested gitignore
    - Migration path for existing projects with slice branches
+
+## Drift From Original Decision
+
+*Audited 2026-05-02. Items the ADR claims were deleted that are still present in the codebase:*
+
+| Item | Status | File:Line | Cleanup Pending |
+|------|--------|-----------|-----------------|
+| `git-self-heal.ts` (whole file) | **Still present** | `src/resources/extensions/sf/git-self-heal.ts:1–142` | File is 142 lines; exports `abortAndReset()` and `formatGitError()`. The ADR claimed ~86 lines deleted. Delete entire file and migrate any callers of `abortAndReset()` to in-place reset logic. |
+| `smartStage()` | **Still present** | `src/resources/extensions/sf/git-service.ts:576` | Still has `_runtimeFilesCleanedUp` migration logic, `SF_MILESTONE_LOCK` parallel-scope exclusions, and 49+ lines of runtime exclusion. Simplify as described in Consequences section. |
+| `shouldUseWorktreeIsolation()` | **Still present** | `src/resources/extensions/sf/auto.ts:357` | ADR requires single-mode worktree-always behavior; this function still exists and defaults to `false` (worktree off unless explicit opt-in). Branch-mode fallback persists. Remove after deprecating `git.isolation: "branch"`. |
+| `getSliceBranchName()` | **Still present** | `src/resources/extensions/sf/worktree.ts:261` | Still used by `workspace-index.ts:156` to record historical branch names. Evaluate whether this is still needed or can be removed. |
+| `MergeConflictError` + fix-merge JSDoc | **Partially present** | `src/resources/extensions/sf/git-service.ts:199–225` | `MergeConflictError` class and a JSDoc comment referencing "dispatch a fix-merge session" remain. The `fix-merge.md` prompt template is deleted; no active dispatch loop found. Remove the JSDoc reference and evaluate if `MergeConflictError` is still needed (it is — used by `slice-cadence.ts`). |
+
+### Items Confirmed Deleted
+
+- `mergeSliceToMilestone()` — not found anywhere in the codebase.
+- Original `mergeSliceToMain()` (branch-era, from `git-service.ts`) — deleted. A *new* `mergeSliceToMain()` exists at `src/resources/extensions/sf/slice-cadence.ts:92` but was added post-ADR for the slice-cadence collapse feature (#4765) and is architecturally consistent with the branchless model.
+- `fix-merge.md` prompt template — deleted (no file at `src/resources/extensions/sf/prompts/fix-merge.md`).
+- Conflict categorization (~80 lines) — not found.
+- `withMergeHeal()` — not found.
+- `ensureSliceBranch()` / `switchToMain()` / `getMergeToMainMode()` — not found.
+
+### Current Authoritative Merge Path
+
+The current milestone→main merge implementation is `mergeMilestoneToMain()` at `src/resources/extensions/sf/auto-worktree.ts:1616`. It performs squash-merge after auto-committing dirty worktree state, reconciling the worktree DB, and running a pre-flight rebase. It does not use slice branches, `withMergeHeal`, or conflict categorization.
diff --git a/docs/dev/ADR-014-singularity-knowledge-and-agent-platform.md b/docs/dev/ADR-014-singularity-knowledge-and-agent-platform.md
index 52190c791..ee2dce7a6 100644
--- a/docs/dev/ADR-014-singularity-knowledge-and-agent-platform.md
+++ b/docs/dev/ADR-014-singularity-knowledge-and-agent-platform.md
@@ -2,6 +2,7 @@
 
 **Date**: 2026-04-29
 **Status**: proposed (deferred — capture for staged execution)
+**Revised**: 2026-05-02 — Phase 4 cancelled, see [ADR-019](./ADR-019-workspace-vm-convergence.md)
 
 ## Context
 
@@ -12,7 +13,7 @@ Two trajectories converge:
 - **Knowledge federates** — anti-patterns, learnings, contracts should be reachable across sf instances and across other agent products on the tailnet (Hermes, OpenClaw, Claude Code, Cursor).
 - **Persistent agents centralise** — long-lived cross-project agents (code-reviewer with cross-project memory, memory-curator, security-auditor, build-watch) are too heavy and too cross-cutting to live per-project.
 
-These two needs collapse into one service: the **Singularity Knowledge + Agent Platform** — a single Go server hosting the federated memory store *and* the central persistent-agent runtime.
+These two needs collapse into one service: the **Singularity Knowledge + Agent Platform** — a single Go server hosting the federated memory store *and* the central persistent-agent runtime. *(Note: the persistent-agent runtime portion — Phase 4 — has since been cancelled by [ADR-019](./ADR-019-workspace-vm-convergence.md). This ADR's active scope is the knowledge layer only, Phases 0–3.)*
 
 This ADR fixes the stack.
 
@@ -23,7 +24,7 @@ The implementation arm of this ADR lives in [`singularity-memory/MIGRATION.md`](
 - **Language: Go.**
 - **Storage backbone: Postgres + vchord** (existing) — accessed from Go via `pgx`. No data migration; same schema, same vchord index.
 - **Identity / auth / sync layer: `charmbracelet/charm`-server patterns** — SSH-key identity, JWT issuance, encrypted KV for user-level prefs and config. Adopted as ported library code; not run as a sidecar.
-- **Agent runtime: `charmbracelet/fantasy`** — multi-provider LLM access (Anthropic, OpenAI, Google, Bedrock, OpenRouter, etc. via `catwalk`). Used for embeddings/summarisation today; for full central persistent agents tomorrow.
+- **Agent runtime: `charmbracelet/fantasy`** — multi-provider LLM access (Anthropic, OpenAI, Google, Bedrock, OpenRouter, etc. via `catwalk`). Used for embeddings/summarisation today. *(The original plan to grow this into a full central persistent-agent runtime — Phase 4 — is cancelled by [ADR-019](./ADR-019-workspace-vm-convergence.md). `fantasy` is retained for embeddings/summarisation within the knowledge layer only.)*
 - **HTTP API: Go `net/http` + chi or echo router**, serving the *exact* current OpenAPI contract.
 - **MCP server: same wire protocol** as today's Python implementation. Clients (sf, Hermes, OpenClaw, Claude Code, Cursor) keep working unchanged.
 - **CLI scaffolding: `charmbracelet/fang`.**
@@ -47,7 +48,7 @@ The implementation arm of this ADR lives in [`singularity-memory/MIGRATION.md`](
 
 ### Agent runtime
 
-- **Direct SDK calls (`anthropic-sdk-go`, `openai-go`, `go-genai`).** Simplest for today's narrow LLM use (embeddings + summarisation). But future central persistent agents need agent-loop semantics (multi-turn, tool calls); building those on raw SDKs reinvents fantasy's abstractions. Rejected — foundation bet.
+- **Direct SDK calls (`anthropic-sdk-go`, `openai-go`, `go-genai`).** Simplest for today's narrow LLM use (embeddings + summarisation). But future central persistent agents need agent-loop semantics (multi-turn, tool calls); building those on raw SDKs reinvents fantasy's abstractions. Rejected — foundation bet. *(Phase 4 is now cancelled by [ADR-019](./ADR-019-workspace-vm-convergence.md), so the persistent-agent motivation no longer applies; however `fantasy` is still chosen for its clean multi-provider API for embeddings/summarisation.)*
 - **Build our own agent runtime in Go.** Pure NIH. Rejected.
 - **`charmbracelet/fantasy`.** ← chosen. 730 stars, actively developed, clean API, multi-provider via `catwalk`.
 
@@ -55,7 +56,7 @@ The implementation arm of this ADR lives in [`singularity-memory/MIGRATION.md`](
 
 **Positive**
 
-- **Foundation is right** for central persistent agents (sf SPEC §17). Adding new agents means defining their tools and system prompt, not rebuilding the runtime.
+- **Foundation is right** for the knowledge layer. *(The original "foundation for central persistent agents" rationale is superseded — Phase 4 is cancelled by [ADR-019](./ADR-019-workspace-vm-convergence.md). Persistent agents now live as Firecracker VM snapshots managed by ACE.)*
 - **Single static Go binary** is operationally simpler than Python uv/venv + Alembic + worker on each deployment host.
 - **Charm ecosystem alignment** with sf-worker (ADR-013), flight recorder (ADR-015), Charm TUI client (ADR-017). One language for the new-services tier.
 - **Wire contract preserved** — clients are zero-touch.
@@ -75,7 +76,7 @@ The implementation arm of this ADR lives in [`singularity-memory/MIGRATION.md`](
 - *Risk:* `fantasy` API churn during the migration.
   - *Mitigation:* pin a version; one planned upgrade midway through the migration.
 - *Risk:* central agents prove unworkable as a model and we've over-built the foundation.
-  - *Mitigation:* the foundation cost is incremental (fantasy ≈ raw SDK + a thin abstraction). Worst case we use fantasy for embeddings only and never grow it. No wasted bet.
+  - *Mitigation:* the foundation cost is incremental (fantasy ≈ raw SDK + a thin abstraction). Worst case we use fantasy for embeddings only and never grow it. No wasted bet. *(Moot — Phase 4 is cancelled by [ADR-019](./ADR-019-workspace-vm-convergence.md); fantasy stays scoped to the knowledge layer.)*
 
 ## Out of Scope
 
@@ -92,10 +93,26 @@ The implementation arm of this ADR lives in [`singularity-memory/MIGRATION.md`](
 | 1 | Greenfield Go scaffold parallel to Python; first endpoint (`GET /v1/banks`) | 2–3 weeks |
 | 2 | Endpoint parity (recall is the critical gate) | 4–8 weeks |
 | 3 | Worker + admin UI (`pony` + `ultraviolet` on `wish`) | 2–3 weeks |
-| 4 | Central persistent-agent host (depends on sf SPEC §17 scoping) | variable |
+| ~~4~~ | ~~Central persistent-agent host~~ | ~~variable~~ |
 | 5 | Python deprecation | 1 week |
 
-Total: ~12 weeks for Phases 0–3 + Phase 5; Phase 4 lands when sf-side agent layer is scoped.
+Total: ~12 weeks for Phases 0–3 + Phase 5. Phase 4 is cancelled — see section below.
+
+## Phase 4 — Cancelled (See [ADR-019](./ADR-019-workspace-vm-convergence.md))
+
+Phase 4 was originally planned as a "central persistent-agent runtime" built on `charmbracelet/fantasy` inside singularity-memory's Go server. [ADR-019](./ADR-019-workspace-vm-convergence.md) (Workspace VM Convergence, 2026-05-01) supersedes this plan entirely.
+
+**What replaced it:** Persistent agents now live as **Firecracker VM snapshots managed by ACE**'s orchestration layer. A "persistent agent" is a named VM snapshot: restore it, and the agent wakes with its full memory and context intact. singularity-memory's scope is now strictly the knowledge layer (Phases 0–3). See ADR-019 § "ADR-014 Phase 4 is reassigned" for the authoritative statement.
+
+### Historical: Original Phase 4 Plan
+
+> *The content below is the original Phase 4 design, preserved as a historical record. It is **not** the current plan.*
+
+The original Phase 4 called for singularity-memory's Go server to host a central persistent-agent runtime using `charmbracelet/fantasy`. Long-lived cross-project agents (code-reviewer, memory-curator, security-auditor, build-watch) would run there, with their state managed by the same Postgres store. This depended on sf SPEC §17 scoping being completed ("status NEW" at ADR-014's writing date).
+
+The rationale for building this in singularity-memory was ecosystem alignment with `fantasy` + `charm-server` + `wish` and avoiding per-project agent redundancy. The timeline was listed as "variable" because SPEC §17 had not been fully scoped.
+
+ADR-019 made this moot by choosing a cleaner isolation model (hypervisor-level VM snapshots) that is language-agnostic inside the VM, multi-tenant by construction, and owned by ACE rather than a shared Go server.
 
 ## References
 
diff --git a/docs/dev/ADR-019-workspace-vm-convergence.md b/docs/dev/ADR-019-workspace-vm-convergence.md
index ed6cbe91e..9e5c3d3e9 100644
--- a/docs/dev/ADR-019-workspace-vm-convergence.md
+++ b/docs/dev/ADR-019-workspace-vm-convergence.md
@@ -2,6 +2,7 @@
 
 **Status:** Proposed
 **Date:** 2026-05-01
+**Revised:** 2026-05-02 — wire-format scope superseded by ADR-020
 **Deciders:** Mikael Hugo
 **Context repos:** `singularity-forge` (SF), `ace-coder` (ACE)
 
@@ -175,7 +176,9 @@ workspace VM primitive is stable.
 
 ## MCP scope
 
-Internal services use typed direct clients (gRPC for first-party). MCP is reserved
+> **Superseded by ADR-020:** This section's proposal to use MCP for internal service wires is replaced. ADR-020 mandates **gRPC** for first-party services (SF, ACE, memory). MCP is reserved for **external coding tools** (Claude Code, Cursor) only. The original analysis below is preserved as historical context.
+
+[Originally proposed: MCP for internal services — superseded by ADR-020 in favor of gRPC.] Internal services use typed direct clients (gRPC for first-party). MCP is reserved
 for external coding tools (Claude Code, Cursor) that don't share our build system.
 See [ADR-020](./ADR-020-internal-wire-architecture.md) for the full wire-format table and rationale.
 
@@ -190,7 +193,8 @@ See [ADR-020](./ADR-020-internal-wire-architecture.md) for the full wire-format
 
 ### Phase 2 — Federated memory for ACE (near-term, ADR-012 Tier 1)
 - ACE connects to singularity-memory via a typed Python client (generated from
-  the Go API — not MCP). Internal services do not pay the MCP tax.
+  the Go API — not MCP). Internal services do not pay the MCP tax. [Wire format
+  confirmed by ADR-020: gRPC for first-party services.]
 - **SF stays local.** SF is single-machine, single-user, local-first by design.
   `memory-store.ts` continues to work on `.sf/memory/`; no remote mode wired in
   SF core. When SF runs inside an ACE-managed workspace, the workspace surfaces
diff --git a/packages/pi-coding-agent/src/core/slash-commands.ts b/packages/pi-coding-agent/src/core/slash-commands.ts
index bcde22d9b..e3e0a827d 100644
--- a/packages/pi-coding-agent/src/core/slash-commands.ts
+++ b/packages/pi-coding-agent/src/core/slash-commands.ts
@@ -39,5 +39,6 @@ export const BUILTIN_SLASH_COMMANDS: ReadonlyArray<BuiltinSlashCommand> = [
 	{ name: "edit-mode", description: "Toggle edit mode (standard/hashline)" },
 	{ name: "terminal", description: "Run a shell command directly (e.g. /terminal ping -c3 1.1.1.1)" },
 	{ name: "stop", description: "Stop the currently running response" },
+	{ name: "exit", description: "Quit pi" },
 	{ name: "quit", description: "Quit pi" },
 ];
diff --git a/packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.test.ts b/packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.test.ts
index 78f6846ac..f9a7d1d8b 100644
--- a/packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.test.ts
+++ b/packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.test.ts
@@ -23,6 +23,7 @@ function createHost(options: HostOptions = {}) {
 	let editorText = "";
 	let settingsOpened = 0;
 	let aborts = 0;
+	let shutdowns = 0;
 	const statuses: string[] = [];
 	let pendingDisplayUpdates = 0;
 	let renderRequests = 0;
@@ -67,6 +68,9 @@ function createHost(options: HostOptions = {}) {
 				settingsOpened += 1;
 			},
 			showStatus: host.showStatus,
+			shutdown: async () => {
+				shutdowns += 1;
+			},
 		}),
 		handleBashCommand: async () => {},
 		showWarning(message: string) {
@@ -113,6 +117,7 @@ function createHost(options: HostOptions = {}) {
 		getEditorText: () => editorText,
 		getSettingsOpened: () => settingsOpened,
 		getAborts: () => aborts,
+		getShutdowns: () => shutdowns,
 		statuses,
 		getPendingDisplayUpdates: () => pendingDisplayUpdates,
 		getRenderRequests: () => renderRequests,
@@ -147,6 +152,17 @@ test("input-controller: built-in slash commands stay in TUI dispatch", async ()
 	);
 });
 
+test("input-controller: /exit is a built-in shutdown alias", async () => {
+	const { host, prompted, errors, getEditorText, getShutdowns } = createHost();
+
+	await host.defaultEditor.onSubmit("/exit");
+
+	assert.equal(getShutdowns(), 1);
+	assert.deepEqual(prompted, []);
+	assert.deepEqual(errors, []);
+	assert.equal(getEditorText(), "");
+});
+
 test("input-controller: /stop aborts the current response", async () => {
 	const { host, prompted, errors, statuses, getAborts, getEditorText } =
 		createHost();
diff --git a/packages/pi-coding-agent/src/modes/interactive/slash-command-handlers.ts b/packages/pi-coding-agent/src/modes/interactive/slash-command-handlers.ts
index 203a51bc9..c4250e939 100644
--- a/packages/pi-coding-agent/src/modes/interactive/slash-command-handlers.ts
+++ b/packages/pi-coding-agent/src/modes/interactive/slash-command-handlers.ts
@@ -219,6 +219,15 @@ export async function dispatchSlashCommand(
 		ctx.showSessionSelector();
 		return true;
 	}
+	if (text === "/exit") {
+		const extensionExit = ctx.session.extensionRunner?.getCommand("exit");
+		if (extensionExit && ctx.session.extensionRunner) {
+			await extensionExit.handler("", ctx.session.extensionRunner.createCommandContext());
+		} else {
+			await ctx.shutdown();
+		}
+		return true;
+	}
 	if (text === "/quit") {
 		await ctx.shutdown();
 		return true;
diff --git a/src/resources/extensions/sf/auto-worktree.ts b/src/resources/extensions/sf/auto-worktree.ts
index 7bd68861b..b439beb75 100644
--- a/src/resources/extensions/sf/auto-worktree.ts
+++ b/src/resources/extensions/sf/auto-worktree.ts
@@ -7,6 +7,7 @@
  */
 
 import { execFileSync } from "node:child_process";
+import { randomUUID } from "node:crypto";
 import {
 	cpSync,
 	existsSync,
@@ -57,6 +58,7 @@ import {
 	isDbAvailable,
 	reconcileWorktreeDb,
 } from "./sf-db.js";
+import { emitJournalEvent } from "./journal.js";
 import { logError, logWarning } from "./workflow-logger.js";
 import { detectWorktreeName, nudgeGitBranchCache } from "./worktree.js";
 import {
@@ -66,6 +68,7 @@ import {
 	resolveGitDir,
 	worktreePath,
 } from "./worktree-manager.js";
+import { isInsideWorktree } from "./repo-identity.js";
 
 const sfHome = process.env.SF_HOME || join(homedir(), ".sf");
 const PROJECT_PREFERENCES_FILE = "PREFERENCES.md";
@@ -1204,6 +1207,26 @@ export function createAutoWorktree(
 	basePath: string,
 	milestoneId: string,
 ): string {
+	// Guard: refuse to create a worktree from inside an existing worktree.
+	// Nested worktrees corrupt state on merge-back and are never intentional.
+	if (isInsideWorktree(basePath)) {
+		emitJournalEvent(basePath, {
+			ts: new Date().toISOString(),
+			flowId: randomUUID(),
+			seq: 0,
+			eventType: "worktree-create-failed",
+			data: {
+				milestoneId,
+				reason: "nested-worktree-rejected",
+				basePath,
+			},
+		});
+		throw new SFError(
+			SF_GIT_ERROR,
+			`cannot create a nested worktree from inside an existing worktree: ${basePath}`,
+		);
+	}
+
 	const branch = autoWorktreeBranch(milestoneId);
 
 	// Check if the milestone branch already exists — it survives auto-mode
diff --git a/src/resources/extensions/sf/journal.ts b/src/resources/extensions/sf/journal.ts
index 31846c674..a12e66134 100644
--- a/src/resources/extensions/sf/journal.ts
+++ b/src/resources/extensions/sf/journal.ts
@@ -63,7 +63,9 @@ export type JournalEventType =
 	| "milestone-resquash"
 	// dispatch telemetry — measure agent/subagent invocation frequency and shape
 	| "subagent-invoked"
-	| "subagent-completed";
+	| "subagent-completed"
+	// #6 — divergence cap enforcement
+	| "worktree-divergence-warning";
 
 /** A single structured event in the journal. */
 export interface JournalEntry {
diff --git a/src/resources/extensions/sf/native-git-bridge.ts b/src/resources/extensions/sf/native-git-bridge.ts
index 1f8efa215..35a4b5c70 100644
--- a/src/resources/extensions/sf/native-git-bridge.ts
+++ b/src/resources/extensions/sf/native-git-bridge.ts
@@ -1484,6 +1484,25 @@ export function nativeUnpushedCount(basePath: string, branch: string): number {
 	}
 }
 
+/**
+ * Count commits that are ahead of and behind a reference (e.g. main branch).
+ * Returns { commitsAhead, commitsBehind } from the perspective of `worktreePath`.
+ *
+ * commitsAhead  = commits in HEAD that are not in mainRef  (HEAD..mainRef inverse)
+ * commitsBehind = commits in mainRef not yet in HEAD        (mainRef..HEAD inverse)
+ *
+ * Fallback: `git rev-list --count <ref>..HEAD` and the inverse.
+ */
+export function getCommitsBehindMain(
+	worktreePath: string,
+	mainRef: string,
+): { commitsAhead: number; commitsBehind: number } {
+	// nativeCommitCountBetween is already available and backed by native or CLI
+	const commitsAhead = nativeCommitCountBetween(worktreePath, mainRef, "HEAD");
+	const commitsBehind = nativeCommitCountBetween(worktreePath, "HEAD", mainRef);
+	return { commitsAhead, commitsBehind };
+}
+
 // ─── Re-exports for type consumers ──────────────────────────────────────
 
 export type {
diff --git a/src/resources/extensions/sf/orphan-worktree-sweep.ts b/src/resources/extensions/sf/orphan-worktree-sweep.ts
new file mode 100644
index 000000000..82a33dd8d
--- /dev/null
+++ b/src/resources/extensions/sf/orphan-worktree-sweep.ts
@@ -0,0 +1,185 @@
+/**
+ * SF Orphan Worktree Sweep
+ *
+ * Detects orphaned worktree directories left behind by crashed or killed units
+ * and either leaves them intact (resumable) or removes them (broken).
+ *
+ * Called at session_start to ensure stale worktrees from prior crashes don't
+ * accumulate indefinitely.
+ *
+ * Triage logic:
+ *   Active    — auto.lock present and PID alive  → leave alone
+ *   Resumable — no active lock, but .git file is valid     → leave intact, journal
+ *   Broken    — .git missing or unreadable               → prune, journal
+ */
+
+import { randomUUID } from "node:crypto";
+import { existsSync, lstatSync, readdirSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { emitJournalEvent } from "./journal.js";
+import { removeWorktree, worktreesDir, worktreePath } from "./worktree-manager.js";
+
+// ─── Types ───────────────────────────────────────────────────────────────────
+
+export interface SweepResult {
+	/** Milestone IDs whose worktrees were left intact for operator resume. */
+	resumed: string[];
+	/** Milestone IDs whose worktrees were removed (broken structure). */
+	pruned: string[];
+	/** Per-worktree errors that did not stop the sweep. */
+	errors: { id: string; reason: string }[];
+}
+
+// ─── Internal Helpers ─────────────────────────────────────────────────────────
+
+/**
+ * Read the auto.lock file for a worktree and return the PID, or null if absent.
+ * The lock lives at <worktreeDir>/.sf/auto.lock (the worktree has its own .sf/).
+ */
+function readWorktreeLockPid(worktreeDir: string): number | null {
+	const lockPath = join(worktreeDir, ".sf", "auto.lock");
+	if (!existsSync(lockPath)) return null;
+	try {
+		const raw = readFileSync(lockPath, "utf-8");
+		const data = JSON.parse(raw) as { pid?: unknown };
+		return typeof data.pid === "number" ? data.pid : null;
+	} catch {
+		return null;
+	}
+}
+
+/**
+ * Returns true if the given PID is alive in this OS process table.
+ * Uses signal 0 — POSIX / Node standard liveness probe.
+ */
+function isPidAlive(pid: number): boolean {
+	try {
+		process.kill(pid, 0);
+		return true;
+	} catch {
+		return false;
+	}
+}
+
+/**
+ * Returns true if the worktree at `wtPath` has a structurally valid git pointer:
+ * a `.git` *file* (not a directory) whose content starts with "gitdir:".
+ *
+ * A real git worktree always has a .git file. A .git directory means it's a
+ * standalone repo nested inside (not a registered worktree). Either way the
+ * worktree is not structurally healthy as an SF worktree.
+ */
+function isStructurallyHealthy(wtPath: string): boolean {
+	const gitPath = join(wtPath, ".git");
+	if (!existsSync(gitPath)) return false;
+	try {
+		const stat = lstatSync(gitPath);
+		if (!stat.isFile()) return false;
+		const content = readFileSync(gitPath, "utf-8").trim();
+		return content.startsWith("gitdir:");
+	} catch {
+		return false;
+	}
+}
+
+// ─── Public API ───────────────────────────────────────────────────────────────
+
+/**
+ * Sweep `.sf/worktrees/` for orphaned worktrees and triage each one.
+ *
+ * - Active (PID alive)  → skipped entirely.
+ * - Resumable (healthy) → left intact; operator-visible journal event emitted.
+ * - Broken (no .git)    → removed via removeWorktree(); journal event emitted.
+ *
+ * Never throws. Each per-worktree error is accumulated in `errors[]`.
+ * Idempotent: running twice with no orphans returns all-empty arrays both times.
+ *
+ * @param basePath  The project root (not the worktree path).
+ */
+export function sweepOrphanWorktrees(basePath: string): SweepResult {
+	const result: SweepResult = { resumed: [], pruned: [], errors: [] };
+
+	const wtDir = worktreesDir(basePath);
+	if (!existsSync(wtDir)) return result;
+
+	let entries: string[];
+	try {
+		entries = readdirSync(wtDir, { withFileTypes: true })
+			.filter((d) => d.isDirectory())
+			.map((d) => d.name);
+	} catch (err) {
+		result.errors.push({
+			id: "<worktrees-dir>",
+			reason: `readdirSync failed: ${err instanceof Error ? err.message : String(err)}`,
+		});
+		return result;
+	}
+
+	for (const id of entries) {
+		try {
+			const wtPath = worktreePath(basePath, id);
+
+			// ── Active check ──────────────────────────────────────────────────
+			const pid = readWorktreeLockPid(wtPath);
+			if (pid !== null && isPidAlive(pid)) {
+				// In-flight unit owns this worktree — leave it completely alone.
+				continue;
+			}
+
+			// ── Structural health ─────────────────────────────────────────────
+			if (isStructurallyHealthy(wtPath)) {
+				// Orphan but intact — operator may want to resume or inspect.
+				result.resumed.push(id);
+				try {
+					emitJournalEvent(basePath, {
+						ts: new Date().toISOString(),
+						flowId: randomUUID(),
+						seq: 0,
+						eventType: "worktree-orphaned",
+						data: {
+							milestoneId: id,
+							reason: "resumable",
+							worktreeDirExists: true,
+							detectedAt: new Date().toISOString(),
+						},
+					});
+				} catch {
+					// telemetry failure must not abort sweep
+				}
+			} else {
+				// Broken worktree — prune it.
+				const detail = !existsSync(join(wtPath, ".git"))
+					? "missing .git file"
+					: "invalid .git content";
+
+				removeWorktree(basePath, id, { deleteBranch: false, force: true });
+				result.pruned.push(id);
+
+				try {
+					emitJournalEvent(basePath, {
+						ts: new Date().toISOString(),
+						flowId: randomUUID(),
+						seq: 0,
+						eventType: "worktree-orphaned",
+						data: {
+							milestoneId: id,
+							reason: "broken-pruned",
+							worktreeDirExists: false,
+							detail,
+							detectedAt: new Date().toISOString(),
+						},
+					});
+				} catch {
+					// telemetry failure must not abort sweep
+				}
+			}
+		} catch (err) {
+			result.errors.push({
+				id,
+				reason: err instanceof Error ? err.message : String(err),
+			});
+		}
+	}
+
+	return result;
+}
diff --git a/src/resources/extensions/sf/tests/auto-worktree-nested-guard.test.ts b/src/resources/extensions/sf/tests/auto-worktree-nested-guard.test.ts
new file mode 100644
index 000000000..317d64d2a
--- /dev/null
+++ b/src/resources/extensions/sf/tests/auto-worktree-nested-guard.test.ts
@@ -0,0 +1,150 @@
+/**
+ * auto-worktree-nested-guard.test.ts
+ *
+ * Verifies that createAutoWorktree() refuses to create a nested worktree
+ * when basePath is itself a git worktree (.git file, not directory).
+ */
+
+import assert from "node:assert/strict";
+import {
+	mkdirSync,
+	mkdtempSync,
+	readdirSync,
+	readFileSync,
+	rmSync,
+	writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, test } from "vitest";
+
+import { SFError } from "../errors.ts";
+import type { JournalEntry } from "../journal.ts";
+import { createAutoWorktree } from "../auto-worktree.ts";
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+/** Write a fake .git file so the directory looks like a git worktree. */
+function makeWorktreeDir(dir: string): void {
+	writeFileSync(
+		join(dir, ".git"),
+		"gitdir: /some/repo/.git/worktrees/fake-wt\n",
+		"utf-8",
+	);
+}
+
+/** Read all journal entries from a temp .sf/journal directory. */
+function readJournalEntries(basePath: string): JournalEntry[] {
+	const journalDir = join(basePath, ".sf", "journal");
+	try {
+		const files = readdirSync(journalDir)
+			.filter((f) => f.endsWith(".jsonl"))
+			.sort();
+		const entries: JournalEntry[] = [];
+		for (const file of files) {
+			const raw = readFileSync(join(journalDir, file), "utf-8");
+			for (const line of raw.split("\n")) {
+				if (!line.trim()) continue;
+				entries.push(JSON.parse(line) as JournalEntry);
+			}
+		}
+		return entries;
+	} catch {
+		return [];
+	}
+}
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+describe("createAutoWorktree nested-worktree guard", () => {
+	let tmp: string;
+
+	beforeEach(() => {
+		tmp = mkdtempSync(join(tmpdir(), "sf-nested-wt-guard-"));
+	});
+
+	afterEach(() => {
+		rmSync(tmp, { recursive: true, force: true });
+	});
+
+	test("throws SFError when basePath is a git worktree", () => {
+		makeWorktreeDir(tmp);
+
+		assert.throws(
+			() => createAutoWorktree(tmp, "M001"),
+			(err: unknown) => {
+				assert.ok(err instanceof SFError, "should be an SFError");
+				return true;
+			},
+		);
+	});
+
+	test("error message mentions 'nested worktree' and the offending basePath", () => {
+		makeWorktreeDir(tmp);
+
+		assert.throws(
+			() => createAutoWorktree(tmp, "M001"),
+			(err: unknown) => {
+				assert.ok(err instanceof Error);
+				assert.ok(
+					err.message.includes("nested worktree"),
+					`expected 'nested worktree' in message, got: ${err.message}`,
+				);
+				assert.ok(
+					err.message.includes(tmp),
+					`expected basePath in message, got: ${err.message}`,
+				);
+				return true;
+			},
+		);
+	});
+
+	test("emits worktree-create-failed journal event with nested-worktree-rejected reason", () => {
+		// Ensure .sf/journal directory is writable for the journal emit.
+		mkdirSync(join(tmp, ".sf", "journal"), { recursive: true });
+		makeWorktreeDir(tmp);
+
+		assert.throws(() => createAutoWorktree(tmp, "M001"));
+
+		const entries = readJournalEntries(tmp);
+		const failed = entries.find(
+			(e) => e.eventType === "worktree-create-failed",
+		);
+		assert.ok(failed, "worktree-create-failed event should be emitted");
+		assert.equal(
+			failed!.data?.reason,
+			"nested-worktree-rejected",
+			"reason must be nested-worktree-rejected",
+		);
+		assert.equal(
+			failed!.data?.milestoneId,
+			"M001",
+			"milestoneId must be recorded",
+		);
+		assert.equal(
+			failed!.data?.basePath,
+			tmp,
+			"basePath must be recorded in event data",
+		);
+	});
+
+	test("succeeds (does not throw) when basePath is a regular repo directory (control case)", () => {
+		// Simulate a real repo: .git is a *directory*, not a file.
+		mkdirSync(join(tmp, ".git"), { recursive: true });
+
+		// createAutoWorktree will fail with a git error (no real git binary
+		// operations succeed on this fake repo), but it must NOT throw the
+		// nested-worktree guard error — i.e. it must get past the guard.
+		assert.throws(
+			() => createAutoWorktree(tmp, "M001"),
+			(err: unknown) => {
+				assert.ok(err instanceof Error);
+				assert.ok(
+					!err.message.includes("nested worktree"),
+					`guard must NOT fire for a regular repo; got: ${err.message}`,
+				);
+				return true;
+			},
+		);
+	});
+});
diff --git a/src/resources/extensions/sf/tests/orphan-worktree-sweep.test.ts b/src/resources/extensions/sf/tests/orphan-worktree-sweep.test.ts
new file mode 100644
index 000000000..9f9a27774
--- /dev/null
+++ b/src/resources/extensions/sf/tests/orphan-worktree-sweep.test.ts
@@ -0,0 +1,277 @@
+/**
+ * Tests for orphan-worktree-sweep.ts
+ *
+ * Uses a tmpdir for a fake project root. We don't need real git plumbing because
+ * the sweep only reads the filesystem (auto.lock for PID, .git file for structure).
+ * removeWorktree is mocked where needed to avoid git side-effects.
+ */
+
+import assert from "node:assert/strict";
+import {
+	existsSync,
+	mkdirSync,
+	mkdtempSync,
+	readdirSync,
+	readFileSync,
+	rmSync,
+	writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, test, vi } from "vitest";
+
+// ─── Module under test ───────────────────────────────────────────────────────
+// We import after vi.mock declarations so the mocks are in place.
+
+// Mock removeWorktree so tests don't need a live git repo.
+vi.mock("../worktree-manager.js", async (importOriginal) => {
+	const real = await importOriginal<typeof import("../worktree-manager.js")>();
+	return {
+		...real,
+		removeWorktree: vi.fn(),
+	};
+});
+
+import { sweepOrphanWorktrees } from "../orphan-worktree-sweep.ts";
+import { removeWorktree } from "../worktree-manager.js";
+import type { JournalEntry } from "../journal.js";
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/** Create a minimal fake project tree: <root>/.sf/worktrees/ */
+function makeProject(): string {
+	const root = mkdtempSync(join(tmpdir(), "orphan-sweep-test-"));
+	mkdirSync(join(root, ".sf", "worktrees"), { recursive: true });
+	// Minimal .sf/ so journal writes don't fail
+	mkdirSync(join(root, ".sf", "journal"), { recursive: true });
+	return root;
+}
+
+/**
+ * Create a worktree directory with a valid .git pointer file.
+ * The `gitdir:` target doesn't need to exist for the structural check.
+ */
+function makeHealthyWorktree(root: string, id: string): string {
+	const wtPath = join(root, ".sf", "worktrees", id);
+	mkdirSync(join(wtPath, ".sf"), { recursive: true });
+	writeFileSync(join(wtPath, ".git"), "gitdir: ../../.git/worktrees/" + id + "\n");
+	return wtPath;
+}
+
+/**
+ * Create a worktree directory that is BROKEN — no .git file at all.
+ */
+function makeBrokenWorktree(root: string, id: string): string {
+	const wtPath = join(root, ".sf", "worktrees", id);
+	mkdirSync(join(wtPath, ".sf"), { recursive: true });
+	// Intentionally no .git file
+	return wtPath;
+}
+
+/**
+ * Write a fake auto.lock into a worktree with a given PID.
+ */
+function writeLock(wtPath: string, pid: number): void {
+	writeFileSync(
+		join(wtPath, ".sf", "auto.lock"),
+		JSON.stringify({ pid, startedAt: new Date().toISOString(), unitType: "execute-task", unitId: "T01", unitStartedAt: new Date().toISOString() }),
+	);
+}
+
+/** Read all journal entries from a temp project's .sf/journal directory. */
+function readJournal(root: string): JournalEntry[] {
+	const journalDir = join(root, ".sf", "journal");
+	try {
+		const files = readdirSync(journalDir)
+			.filter((f) => f.endsWith(".jsonl"))
+			.sort();
+		const entries: JournalEntry[] = [];
+		for (const file of files) {
+			const raw = readFileSync(join(journalDir, file), "utf-8");
+			for (const line of raw.split("\n")) {
+				if (!line.trim()) continue;
+				try {
+					entries.push(JSON.parse(line) as JournalEntry);
+				} catch {
+					// skip
+				}
+			}
+		}
+		return entries;
+	} catch {
+		return [];
+	}
+}
+
+// ─── Setup ────────────────────────────────────────────────────────────────────
+
+let projectRoot: string;
+
+beforeEach(() => {
+	vi.clearAllMocks();
+	projectRoot = makeProject();
+});
+
+afterEach(() => {
+	rmSync(projectRoot, { recursive: true, force: true });
+});
+
+// ─── Test cases ───────────────────────────────────────────────────────────────
+
+describe("sweepOrphanWorktrees", () => {
+	// 1. Empty worktrees directory
+	test("empty .sf/worktrees/ returns all-empty arrays, no errors", () => {
+		const result = sweepOrphanWorktrees(projectRoot);
+		assert.deepStrictEqual(result.resumed, []);
+		assert.deepStrictEqual(result.pruned, []);
+		assert.deepStrictEqual(result.errors, []);
+	});
+
+	// 2. Active worktree (PID is our own process — guaranteed alive)
+	test("active worktree (live PID in auto.lock) is left alone", () => {
+		const wtPath = makeHealthyWorktree(projectRoot, "M001");
+		writeLock(wtPath, process.pid); // Our own PID is always alive
+
+		const result = sweepOrphanWorktrees(projectRoot);
+		assert.deepStrictEqual(result.resumed, [], "active worktree must not appear in resumed");
+		assert.deepStrictEqual(result.pruned, [], "active worktree must not appear in pruned");
+		assert.deepStrictEqual(result.errors, []);
+		assert.ok(existsSync(wtPath), "worktree directory must still exist");
+	});
+
+	// 3. Resumable orphan — healthy worktree, no live lock
+	test("resumable orphan is left intact and journaled with reason 'resumable'", () => {
+		makeHealthyWorktree(projectRoot, "M002");
+		// No auto.lock written → no active PID
+
+		const result = sweepOrphanWorktrees(projectRoot);
+		assert.deepStrictEqual(result.resumed, ["M002"]);
+		assert.deepStrictEqual(result.pruned, []);
+		assert.deepStrictEqual(result.errors, []);
+
+		// worktree directory must still exist
+		assert.ok(existsSync(join(projectRoot, ".sf", "worktrees", "M002")));
+
+		// Journal must have a worktree-orphaned event with reason 'resumable'
+		const events = readJournal(projectRoot).filter(
+			(e) => e.eventType === "worktree-orphaned",
+		);
+		assert.equal(events.length, 1, "one orphaned event expected");
+		assert.equal(events[0].data?.milestoneId, "M002");
+		assert.equal(events[0].data?.reason, "resumable");
+	});
+
+	// 4. Broken orphan — missing .git file
+	test("broken orphan (missing .git) is pruned and journaled with reason 'broken-pruned'", () => {
+		makeBrokenWorktree(projectRoot, "M003");
+
+		const result = sweepOrphanWorktrees(projectRoot);
+		assert.deepStrictEqual(result.pruned, ["M003"]);
+		assert.deepStrictEqual(result.resumed, []);
+		assert.deepStrictEqual(result.errors, []);
+
+		// removeWorktree must have been called
+		assert.ok(
+			(removeWorktree as ReturnType<typeof vi.fn>).mock.calls.some(
+				(args) => args[1] === "M003",
+			),
+			"removeWorktree called for M003",
+		);
+
+		// Journal event
+		const events = readJournal(projectRoot).filter(
+			(e) => e.eventType === "worktree-orphaned",
+		);
+		assert.equal(events.length, 1, "one orphaned event expected");
+		assert.equal(events[0].data?.milestoneId, "M003");
+		assert.equal(events[0].data?.reason, "broken-pruned");
+	});
+
+	// 5. Mixed: one active, one resumable, one broken
+	test("mixed scenario: active/resumable/broken triaged correctly", () => {
+		// Active — use current process PID
+		const activeWt = makeHealthyWorktree(projectRoot, "M010");
+		writeLock(activeWt, process.pid);
+
+		// Resumable
+		makeHealthyWorktree(projectRoot, "M011");
+
+		// Broken
+		makeBrokenWorktree(projectRoot, "M012");
+
+		const result = sweepOrphanWorktrees(projectRoot);
+
+		assert.deepStrictEqual(result.resumed, ["M011"]);
+		assert.deepStrictEqual(result.pruned, ["M012"]);
+		assert.deepStrictEqual(result.errors, []);
+
+		// Active worktree still exists
+		assert.ok(existsSync(activeWt), "active worktree directory must survive");
+
+		// removeWorktree called only for broken
+		const calls = (removeWorktree as ReturnType<typeof vi.fn>).mock.calls;
+		assert.ok(
+			calls.some((args) => args[1] === "M012"),
+			"removeWorktree called for broken",
+		);
+		assert.ok(
+			!calls.some((args) => args[1] === "M010"),
+			"removeWorktree NOT called for active",
+		);
+		assert.ok(
+			!calls.some((args) => args[1] === "M011"),
+			"removeWorktree NOT called for resumable",
+		);
+
+		// Two journal events: one resumable, one broken-pruned
+		const events = readJournal(projectRoot).filter(
+			(e) => e.eventType === "worktree-orphaned",
+		);
+		assert.equal(events.length, 2);
+		const reasons = events.map((e) => e.data?.reason as string).sort();
+		assert.deepStrictEqual(reasons, ["broken-pruned", "resumable"]);
+	});
+
+	// 6. Error path — removeWorktree throws; error captured, sweep continues
+	test("removeWorktree throw is captured in errors[] and sweep continues", () => {
+		makeBrokenWorktree(projectRoot, "M020");
+		makeHealthyWorktree(projectRoot, "M021"); // resumable — processed after error
+
+		(removeWorktree as ReturnType<typeof vi.fn>).mockImplementationOnce(() => {
+			throw new Error("simulated git failure");
+		});
+
+		const result = sweepOrphanWorktrees(projectRoot);
+
+		// M020 threw, M021 is resumable — both processed
+		assert.equal(result.errors.length, 1, "error accumulated for M020");
+		assert.equal(result.errors[0].id, "M020");
+		assert.ok(result.errors[0].reason.includes("simulated git failure"));
+
+		// M021 still processed as resumable
+		assert.deepStrictEqual(result.resumed, ["M021"]);
+		assert.deepStrictEqual(result.pruned, []);
+	});
+
+	// 7. No .sf/worktrees/ directory — returns empty result immediately
+	test("no .sf/worktrees/ directory returns empty result", () => {
+		rmSync(join(projectRoot, ".sf", "worktrees"), { recursive: true, force: true });
+
+		const result = sweepOrphanWorktrees(projectRoot);
+		assert.deepStrictEqual(result.resumed, []);
+		assert.deepStrictEqual(result.pruned, []);
+		assert.deepStrictEqual(result.errors, []);
+	});
+
+	// 8. Idempotency — running twice with no orphans returns empty arrays
+	test("idempotent: running twice with no orphans returns empty arrays both times", () => {
+		const r1 = sweepOrphanWorktrees(projectRoot);
+		const r2 = sweepOrphanWorktrees(projectRoot);
+
+		for (const result of [r1, r2]) {
+			assert.deepStrictEqual(result.resumed, []);
+			assert.deepStrictEqual(result.pruned, []);
+			assert.deepStrictEqual(result.errors, []);
+		}
+	});
+});
diff --git a/src/resources/extensions/sf/tests/worktree-divergence.test.ts b/src/resources/extensions/sf/tests/worktree-divergence.test.ts
new file mode 100644
index 000000000..41ead8eec
--- /dev/null
+++ b/src/resources/extensions/sf/tests/worktree-divergence.test.ts
@@ -0,0 +1,318 @@
+/**
+ * worktree-divergence.test.ts — #6 divergence cap enforcement
+ *
+ * Tests for:
+ * - getCommitsBehindMain returns correct counts
+ * - mergeWorktreeToMain emits divergence-warning when commits-behind > threshold
+ * - mergeWorktreeToMain proceeds with merge even when over threshold (warn-and-proceed)
+ * - mergeWorktreeToMain({ autoRebase: true }) rebases and merges when no conflicts
+ * - mergeWorktreeToMain({ autoRebase: true }) throws merge conflict and leaves worktree
+ *   in conflict state when rebase conflicts
+ * - Below-threshold case: no warning emitted
+ */
+
+import assert from "node:assert/strict";
+import { execFileSync } from "node:child_process";
+import {
+	existsSync,
+	mkdirSync,
+	mkdtempSync,
+	readFileSync,
+	rmSync,
+	writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, test } from "vitest";
+
+import { queryJournal } from "../journal.js";
+import { getCommitsBehindMain } from "../native-git-bridge.js";
+import {
+	mergeWorktreeToMain,
+	WORKTREE_DIVERGENCE_CAP,
+	worktreePath,
+} from "../worktree-manager.js";
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+function git(args: string[], cwd: string): string {
+	return execFileSync("git", args, {
+		cwd,
+		stdio: ["ignore", "pipe", "pipe"],
+		encoding: "utf-8",
+		env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
+	}).trim();
+}
+
+/** Create a minimal git repo on `main` with one initial commit. */
+function makeBaseRepo(): string {
+	const base = mkdtempSync(join(tmpdir(), "sf-div-test-"));
+	git(["init", "-b", "main"], base);
+	git(["config", "user.name", "Test User"], base);
+	git(["config", "user.email", "test@test.com"], base);
+	// Create .sf dir so journal can write
+	mkdirSync(join(base, ".sf"), { recursive: true });
+	writeFileSync(join(base, "README.md"), "initial\n");
+	git(["add", "."], base);
+	git(["commit", "-m", "chore: init"], base);
+	return base;
+}
+
+/**
+ * Add a git worktree at `.sf/worktrees/<name>` on branch `worktree/<name>`.
+ * Returns the worktree path.
+ */
+function addWorktree(base: string, name: string): string {
+	const wtDir = join(base, ".sf", "worktrees", name);
+	mkdirSync(join(base, ".sf", "worktrees"), { recursive: true });
+	git(["worktree", "add", "-b", `worktree/${name}`, wtDir], base);
+	return wtDir;
+}
+
+/** Commit a file change in a directory. */
+function commitFile(
+	dir: string,
+	filename: string,
+	content: string,
+	message: string,
+): void {
+	writeFileSync(join(dir, filename), content);
+	git(["add", filename], dir);
+	git(["commit", "-m", message], dir);
+}
+
+// ─── getCommitsBehindMain ─────────────────────────────────────────────────────
+
+describe("getCommitsBehindMain", () => {
+	let base: string;
+	let wtPath: string;
+
+	beforeEach(() => {
+		base = makeBaseRepo();
+		wtPath = addWorktree(base, "M001");
+	});
+
+	afterEach(() => {
+		rmSync(base, { recursive: true, force: true });
+	});
+
+	test("returns zero behind when worktree is up-to-date with main", () => {
+		const { commitsAhead, commitsBehind } = getCommitsBehindMain(wtPath, "main");
+		assert.equal(commitsBehind, 0);
+		assert.equal(commitsAhead, 0);
+	});
+
+	test("returns correct commitsBehind when main has advanced", () => {
+		// Advance main by 3 commits (worktree does NOT pick these up)
+		commitFile(base, "a.txt", "a\n", "chore: A");
+		commitFile(base, "b.txt", "b\n", "chore: B");
+		commitFile(base, "c.txt", "c\n", "chore: C");
+
+		const { commitsBehind, commitsAhead } = getCommitsBehindMain(wtPath, "main");
+		assert.equal(commitsBehind, 3);
+		assert.equal(commitsAhead, 0);
+	});
+
+	test("returns correct commitsAhead when worktree has advanced", () => {
+		// Advance worktree by 2 commits
+		commitFile(wtPath, "x.txt", "x\n", "feat: X");
+		commitFile(wtPath, "y.txt", "y\n", "feat: Y");
+
+		const { commitsAhead, commitsBehind } = getCommitsBehindMain(wtPath, "main");
+		assert.equal(commitsAhead, 2);
+		assert.equal(commitsBehind, 0);
+	});
+
+	test("returns both counts when both have diverged", () => {
+		// Advance main by 2
+		commitFile(base, "m1.txt", "m1\n", "chore: main1");
+		commitFile(base, "m2.txt", "m2\n", "chore: main2");
+		// Advance worktree by 1
+		commitFile(wtPath, "w1.txt", "w1\n", "feat: worktree1");
+
+		const { commitsAhead, commitsBehind } = getCommitsBehindMain(wtPath, "main");
+		assert.equal(commitsBehind, 2);
+		assert.equal(commitsAhead, 1);
+	});
+});
+
+// ─── mergeWorktreeToMain — divergence warning ─────────────────────────────────
+
+describe("mergeWorktreeToMain divergence warning", () => {
+	let base: string;
+
+	beforeEach(() => {
+		base = makeBaseRepo();
+	});
+
+	afterEach(() => {
+		rmSync(base, { recursive: true, force: true });
+	});
+
+	test("emits worktree-divergence-warning when commitsBehind > threshold", () => {
+		const name = "M002";
+		const wtDir = addWorktree(base, name);
+
+		// Advance main by WORKTREE_DIVERGENCE_CAP + 1 commits (worktree stays behind)
+		for (let i = 0; i <= WORKTREE_DIVERGENCE_CAP; i++) {
+			commitFile(base, `main-${i}.txt`, `${i}\n`, `chore: main advance ${i}`);
+		}
+
+		// Add one commit to worktree so there is something to merge
+		commitFile(wtDir, "feature.txt", "feature\n", "feat: add feature");
+
+		// Perform merge (warn-and-proceed — may fail on conflict since main diverged)
+		try {
+			mergeWorktreeToMain(base, name, "feat: merge M002");
+		} catch {
+			// A merge conflict is fine for this test; we only care about the warning event
+		}
+
+		const entries = queryJournal(base);
+		const warning = entries.find(
+			(e) => e.eventType === "worktree-divergence-warning",
+		);
+		assert.ok(warning, "worktree-divergence-warning event must be emitted");
+		assert.equal(warning.data?.worktreeId, name);
+		assert.ok(
+			typeof warning.data?.commitsBehind === "number" &&
+				(warning.data.commitsBehind as number) > WORKTREE_DIVERGENCE_CAP,
+			"commitsBehind should exceed the threshold",
+		);
+		assert.equal(warning.data?.threshold, WORKTREE_DIVERGENCE_CAP);
+	});
+
+	test("does NOT emit worktree-divergence-warning when below threshold", () => {
+		const name = "M003";
+		const wtDir = addWorktree(base, name);
+
+		// Advance main by only 2 commits (well below cap)
+		commitFile(base, "m1.txt", "m1\n", "chore: m1");
+		commitFile(base, "m2.txt", "m2\n", "chore: m2");
+
+		// Add a commit to the worktree that doesn't conflict
+		commitFile(wtDir, "feature2.txt", "feature2\n", "feat: feature2");
+
+		try {
+			mergeWorktreeToMain(base, name, "feat: merge M003");
+		} catch {
+			// ignore merge issues
+		}
+
+		const entries = queryJournal(base);
+		const warning = entries.find(
+			(e) => e.eventType === "worktree-divergence-warning",
+		);
+		assert.equal(
+			warning,
+			undefined,
+			"no warning event should be emitted below threshold",
+		);
+	});
+});
+
+// ─── mergeWorktreeToMain — warn-and-proceed ───────────────────────────────────
+
+describe("mergeWorktreeToMain warn-and-proceed", () => {
+	let base: string;
+
+	beforeEach(() => {
+		base = makeBaseRepo();
+	});
+
+	afterEach(() => {
+		rmSync(base, { recursive: true, force: true });
+	});
+
+	test("proceeds with merge (no conflict) even when over threshold", () => {
+		const name = "M004";
+		const wtDir = addWorktree(base, name);
+
+		// Advance main on a different file (no conflict)
+		for (let i = 0; i <= WORKTREE_DIVERGENCE_CAP; i++) {
+			commitFile(base, `main-nc-${i}.txt`, `${i}\n`, `chore: no-conflict ${i}`);
+		}
+
+		// Worktree adds a new file only it touches
+		commitFile(wtDir, "worktree-only.txt", "wt\n", "feat: worktree-only");
+
+		// Should succeed despite being over threshold
+		const result = mergeWorktreeToMain(base, name, "feat: merge M004");
+		assert.equal(result, "feat: merge M004");
+
+		// Verify the warning was emitted
+		const entries = queryJournal(base);
+		const warning = entries.find(
+			(e) => e.eventType === "worktree-divergence-warning",
+		);
+		assert.ok(warning, "warning must be emitted");
+	});
+});
+
+// ─── mergeWorktreeToMain — autoRebase ─────────────────────────────────────────
+
+describe("mergeWorktreeToMain autoRebase", () => {
+	let base: string;
+
+	beforeEach(() => {
+		base = makeBaseRepo();
+	});
+
+	afterEach(() => {
+		rmSync(base, { recursive: true, force: true });
+	});
+
+	test("autoRebase:true rebases and merges successfully when no conflicts", () => {
+		const name = "M005";
+		const wtDir = addWorktree(base, name);
+
+		// Advance main by 3 commits on unique files
+		commitFile(base, "main-r1.txt", "r1\n", "chore: rebase-r1");
+		commitFile(base, "main-r2.txt", "r2\n", "chore: rebase-r2");
+		commitFile(base, "main-r3.txt", "r3\n", "chore: rebase-r3");
+
+		// Worktree adds a unique file
+		commitFile(wtDir, "wt-feature.txt", "feature\n", "feat: wt-feature");
+
+		const result = mergeWorktreeToMain(base, name, "feat: merge M005 rebased", {
+			autoRebase: true,
+		});
+		assert.equal(result, "feat: merge M005 rebased");
+
+		// Confirm the merge landed on main
+		const log = git(["log", "--oneline", "-1"], base);
+		assert.ok(log.includes("feat: merge M005 rebased"), "commit should be on main");
+
+		// The rebase file should exist in main after the squash-merge
+		assert.ok(
+			existsSync(join(base, "wt-feature.txt")),
+			"worktree file should exist in main after merge",
+		);
+	});
+
+	test("autoRebase:true throws SF_MERGE_CONFLICT when rebase has conflicts", () => {
+		const name = "M006";
+		const wtDir = addWorktree(base, name);
+
+		// Both main and worktree modify the same file at the same line
+		commitFile(base, "conflict.txt", "main version\n", "chore: main conflict");
+		commitFile(wtDir, "conflict.txt", "worktree version\n", "feat: wt conflict");
+
+		let threw = false;
+		let errorMessage = "";
+		try {
+			mergeWorktreeToMain(base, name, "feat: merge M006 rebase-conflict", {
+				autoRebase: true,
+			});
+		} catch (err: unknown) {
+			threw = true;
+			errorMessage = err instanceof Error ? err.message : String(err);
+		}
+
+		assert.ok(threw, "should throw when rebase has conflicts");
+		assert.ok(
+			errorMessage.includes("conflict") || errorMessage.includes("Conflict"),
+			`error message should mention conflict, got: ${errorMessage}`,
+		);
+	});
+});
diff --git a/src/resources/extensions/sf/worktree-manager.ts b/src/resources/extensions/sf/worktree-manager.ts
index 84cee57da..866492232 100644
--- a/src/resources/extensions/sf/worktree-manager.ts
+++ b/src/resources/extensions/sf/worktree-manager.ts
@@ -36,6 +36,7 @@ import {
 } from "./errors.js";
 import { SF_RUNTIME_PATTERNS } from "./gitignore.js";
 import {
+	getCommitsBehindMain,
 	nativeBranchDelete,
 	nativeBranchExists,
 	nativeBranchForceReset,
@@ -47,13 +48,20 @@ import {
 	nativeGetCurrentBranch,
 	nativeLogOneline,
 	nativeMergeSquash,
+	nativeRebaseAbort,
 	nativeWorktreeAdd,
 	nativeWorktreeList,
 	nativeWorktreePrune,
 	nativeWorktreeRemove,
 } from "./native-git-bridge.js";
 import { logWarning } from "./workflow-logger.js";
-import { emitCanonicalRootRedirect } from "./worktree-telemetry.js";
+import {
+	emitCanonicalRootRedirect,
+	emitWorktreeDivergenceWarning,
+} from "./worktree-telemetry.js";
+
+/** Commits-behind threshold above which a divergence warning is emitted. */
+export const WORKTREE_DIVERGENCE_CAP = 50;
 
 // ─── Types ─────────────────────────────────────────────────────────────────
 
@@ -792,7 +800,7 @@ function derivePatternsFromRuntime() {
 			paths.push(pattern);
 		} else if (!pattern.includes("*") && !pattern.includes("/")) {
 			exact.push(pattern);
-		} else if (pattern.includes("*")) {
+		} else if (pattern.includes("*") && !pattern.includes("**")) {
 			const prefix = pattern.slice(0, pattern.indexOf("*"));
 			if (prefix && !prefixes.includes(prefix)) {
 				prefixes.push(prefix);
@@ -966,11 +974,21 @@ export function getWorktreeLog(basePath: string, name: string): string {
  * Merge the worktree branch into main using squash merge.
  * Must be called from the main working tree (not the worktree itself).
  * Returns the merge commit message.
+ *
+ * Divergence cap (#6): if the worktree is more than WORKTREE_DIVERGENCE_CAP
+ * commits behind main, a `worktree-divergence-warning` journal event is emitted
+ * before the merge attempt (warn-and-proceed is the default).
+ *
+ * When `autoRebase` is true the worktree branch is rebased onto mainBranch
+ * before the squash-merge. If the rebase produces conflicts the rebase is
+ * aborted and a SF_MERGE_CONFLICT error is thrown so the existing
+ * worktree-merge-failed journal flow handles it.
  */
 export function mergeWorktreeToMain(
 	basePath: string,
 	name: string,
 	commitMessage: string,
+	opts: { autoRebase?: boolean } = {},
 ): string {
 	const branch = worktreeBranchName(name);
 	const mainBranch = nativeDetectMainBranch(basePath);
@@ -983,6 +1001,55 @@ export function mergeWorktreeToMain(
 		);
 	}
 
+	// ─── Divergence cap check (#6) ─────────────────────────────────────────
+	const wtPath = worktreePath(basePath, name);
+	try {
+		const { commitsAhead, commitsBehind } = getCommitsBehindMain(
+			wtPath,
+			mainBranch,
+		);
+		if (commitsBehind > WORKTREE_DIVERGENCE_CAP) {
+			emitWorktreeDivergenceWarning(basePath, name, {
+				commitsAhead,
+				commitsBehind,
+				threshold: WORKTREE_DIVERGENCE_CAP,
+				autoRebase: opts.autoRebase ?? false,
+			});
+			logWarning(
+				"worktree",
+				`worktree ${name} is ${commitsBehind} commits behind ${mainBranch} ` +
+					`(threshold: ${WORKTREE_DIVERGENCE_CAP}). Proceeding with merge.`,
+			);
+		}
+	} catch {
+		// Divergence check is best-effort; never block the merge on telemetry.
+	}
+
+	// ─── Optional auto-rebase ──────────────────────────────────────────────
+	if (opts.autoRebase) {
+		try {
+			execFileSync("git", ["rebase", mainBranch], {
+				cwd: wtPath,
+				stdio: ["ignore", "pipe", "pipe"],
+				encoding: "utf-8",
+				env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
+			});
+		} catch {
+			// Rebase hit conflicts — abort and propagate as a merge conflict so
+			// the caller's worktree-merge-failed flow handles it.
+			try {
+				nativeRebaseAbort(wtPath);
+			} catch {
+				// best-effort abort
+			}
+			throw new SFError(
+				SF_MERGE_CONFLICT,
+				`Auto-rebase of ${branch} onto ${mainBranch} produced conflicts. ` +
+					`Rebase aborted; worktree preserved for manual resolution.`,
+			);
+		}
+	}
+
 	const result = nativeMergeSquash(basePath, branch);
 	if (!result.success) {
 		throw new SFError(
diff --git a/src/resources/extensions/sf/worktree-telemetry.ts b/src/resources/extensions/sf/worktree-telemetry.ts
index 540fe9c15..54e9bfbc8 100644
--- a/src/resources/extensions/sf/worktree-telemetry.ts
+++ b/src/resources/extensions/sf/worktree-telemetry.ts
@@ -120,9 +120,15 @@ export function emitWorktreeOrphaned(
 	milestoneId: string,
 	meta: {
 		flowId?: string;
-		reason: "in-progress-unmerged" | "complete-unmerged" | "stale-branch";
+		reason:
+			| "in-progress-unmerged"
+			| "complete-unmerged"
+			| "stale-branch"
+			| "resumable"
+			| "broken-pruned";
 		commitsAhead?: number;
 		worktreeDirExists?: boolean;
+		detail?: string;
 	},
 ): void {
 	emitJournalEvent(
@@ -133,6 +139,7 @@ export function emitWorktreeOrphaned(
 			reason: meta.reason,
 			commitsAhead: meta.commitsAhead,
 			worktreeDirExists: meta.worktreeDirExists ?? false,
+			detail: meta.detail,
 			detectedAt: now(),
 		}),
 	);
@@ -252,6 +259,33 @@ export function emitMilestoneResquash(
 	);
 }
 
+// #6 — divergence cap enforcement
+
+export function emitWorktreeDivergenceWarning(
+	projectRoot: string,
+	worktreeId: string,
+	meta: {
+		commitsAhead: number;
+		commitsBehind: number;
+		threshold: number;
+		autoRebase: boolean;
+		flowId?: string;
+	},
+): void {
+	emitJournalEvent(
+		projectRoot,
+		baseEntry("worktree-divergence-warning", {
+			worktreeId,
+			commitsAhead: meta.commitsAhead,
+			commitsBehind: meta.commitsBehind,
+			threshold: meta.threshold,
+			autoRebase: meta.autoRebase,
+			detectedAt: now(),
+			flowId: meta.flowId,
+		}),
+	);
+}
+
 // ─── Aggregator ──────────────────────────────────────────────────────────
 
 export interface WorktreeTelemetrySummary {
diff --git a/src/tests/integration/web-command-parity-contract.test.ts b/src/tests/integration/web-command-parity-contract.test.ts
index c00c97f3a..20f0c4a40 100644
--- a/src/tests/integration/web-command-parity-contract.test.ts
+++ b/src/tests/integration/web-command-parity-contract.test.ts
@@ -41,6 +41,8 @@ const EXPECTED_BUILTIN_OUTCOMES = new Map<string, "rpc" | "surface" | "reject">(
 		["thinking", "surface"],
 		["edit-mode", "reject"],
 		["terminal", "reject"],
+		["stop", "reject"],
+		["exit", "reject"],
 		["quit", "reject"],
 	],
 );
@@ -58,6 +60,8 @@ const DEFERRED_BROWSER_REJECTS = [
 	"reload",
 	"edit-mode",
 	"terminal",
+	"stop",
+	"exit",
 	"quit",
 ] as const;
 
@@ -193,17 +197,17 @@ test("registered SF command roots stay on the prompt/extension path", async () =
 	const registeredRoots = await collectRegisteredSfCommandRoots();
 	assert.deepEqual(
 		registeredRoots,
-		["exit", "sf", "kill", "worktree", "wt"],
+		["exit", "kill", "sf", "worktree", "wt"],
 		"browser parity contract only expects the current SF command roots",
 	);
 
 	// Non-sf roots are extension commands that pass through to the bridge.
 	// Derived dynamically so adding a new registration fails this assertion loudly.
-	const nonSfRoots = registeredRoots.filter((r) => r !== "sf");
+	const nonSfRoots = registeredRoots.filter((r) => r !== "sf" && r !== "exit");
 	assert.equal(
 		nonSfRoots.length,
-		4,
-		"expected exactly 4 non-sf passthrough roots; update this count when adding registrations",
+		3,
+		"expected exactly 3 non-sf passthrough roots; update this count when adding registrations",
 	);
 	for (const root of nonSfRoots) {
 		assertPromptPassthrough(`/${root}`);