feat(gsd): enable safety mechanisms by default (snapshots, pre-merge checks) (#2678)

Flip two safety mechanisms from opt-in to opt-out so all users benefit
from rollback protection and merge regression checks without manual
configuration.

- git.snapshots: false → true (creates recovery refs before destructive ops)
- git.pre_merge_check: false → "auto" in solo mode (auto-detects test runner)

Both remain configurable; users can explicitly disable with snapshots: false
or pre_merge_check: false.

Closes #2677

docs/configuration.md

@@ -374,8 +374,8 @@ git:
   auto_push: false            # push commits to remote after committing
   push_branches: false        # push milestone branch to remote
   remote: origin              # git remote name
-  snapshots: false            # WIP snapshot commits during long tasks
-  pre_merge_check: false      # run checks before worktree merge (true/false/"auto")
+  snapshots: true             # WIP snapshot commits during long tasks
+  pre_merge_check: auto       # run checks before worktree merge (true/false/"auto")
   commit_type: feat           # override conventional commit prefix
   main_branch: main           # primary branch name
   merge_strategy: squash      # how worktree branches merge: "squash" or "merge"
@@ -392,8 +392,8 @@ git:
 | `auto_push` | boolean | `false` | Push commits to remote after committing |
 | `push_branches` | boolean | `false` | Push milestone branch to remote |
 | `remote` | string | `"origin"` | Git remote name |
-| `snapshots` | boolean | `false` | WIP snapshot commits during long tasks |
-| `pre_merge_check` | bool/string | `false` | Run checks before merge (`true`/`false`/`"auto"`) |
+| `snapshots` | boolean | `true` | WIP snapshot commits during long tasks |
+| `pre_merge_check` | bool/string | `"auto"` | Run checks before merge (`true`/`false`/`"auto"`) |
 | `commit_type` | string | (inferred) | Override conventional commit prefix (`feat`, `fix`, `refactor`, `docs`, `test`, `chore`, `perf`, `ci`, `build`, `style`) |
 | `main_branch` | string | `"main"` | Primary branch name |
 | `merge_strategy` | string | `"squash"` | How worktree branches merge: `"squash"` (combine all commits) or `"merge"` (preserve individual commits) |

src/resources/extensions/gsd/commands-prefs-wizard.ts

@@ -390,7 +390,7 @@ async function configureGit(ctx: ExtensionCommandContext, prefs: Record<string,
   const gitBooleanFields = [
     { key: "auto_push", label: "Auto-push commits after committing", defaultVal: false },
     { key: "push_branches", label: "Push milestone branches to remote", defaultVal: false },
-    { key: "snapshots", label: "Create WIP snapshot commits during long tasks", defaultVal: false },
+    { key: "snapshots", label: "Create WIP snapshot commits during long tasks", defaultVal: true },
   ] as const;
 
   for (const field of gitBooleanFields) {
@@ -423,7 +423,7 @@ async function configureGit(ctx: ExtensionCommandContext, prefs: Record<string,
   // pre_merge_check
   const currentPreMerge = git.pre_merge_check !== undefined ? String(git.pre_merge_check) : "";
   const preMergeChoice = await ctx.ui.select(
-    `Pre-merge check${currentPreMerge ? ` (current: ${currentPreMerge})` : " (default: false)"}:`,
+    `Pre-merge check${currentPreMerge ? ` (current: ${currentPreMerge})` : " (default: auto)"}:`,
     ["true", "false", "auto", "(keep current)"],
   );
   if (preMergeChoice && preMergeChoice !== "(keep current)") {
@@ -588,7 +588,7 @@ export async function configureMode(ctx: ExtensionCommandContext, prefs: Record<
     if (modeStr.startsWith("solo")) {
       prefs.mode = "solo";
       ctx.ui.notify(
-        "Mode: solo — defaults: auto_push=true, push_branches=false, pre_merge_check=false, merge_strategy=squash, isolation=worktree, unique_milestone_ids=false",
+        "Mode: solo — defaults: auto_push=true, push_branches=false, pre_merge_check=auto, merge_strategy=squash, isolation=worktree, unique_milestone_ids=false",
         "info",
       );
     } else if (modeStr.startsWith("team")) {

src/resources/extensions/gsd/docs/preferences-reference.md

@@ -126,8 +126,8 @@ Setting `prefer_skills: []` does **not** disable skill discovery — it just mea
   - `auto_push`: boolean — automatically push commits to the remote after committing. Default: `false`.
   - `push_branches`: boolean — push the milestone branch to the remote after commits. Default: `false`.
   - `remote`: string — git remote name to push to. Default: `"origin"`.
-  - `snapshots`: boolean — create snapshot commits (WIP saves) during long-running tasks. Default: `false`.
-  - `pre_merge_check`: boolean or `"auto"` — run pre-merge checks before merging a worktree back to the integration branch. `true` always runs, `false` never runs, `"auto"` runs when CI is detected. Default: `false`.
+  - `snapshots`: boolean — create snapshot commits (WIP saves) during long-running tasks. Default: `true`.
+  - `pre_merge_check`: boolean or `"auto"` — run pre-merge checks before merging a worktree back to the integration branch. `true` always runs, `false` never runs, `"auto"` runs when CI is detected. Default: `"auto"`.
   - `commit_type`: string — override the conventional commit type prefix. Must be one of: `feat`, `fix`, `refactor`, `docs`, `test`, `chore`, `perf`, `ci`, `build`, `style`. Default: inferred from diff content.
   - `main_branch`: string — the primary branch name for new git repos (e.g., `"main"`, `"master"`, `"trunk"`). Also used by `getMainBranch()` as the preferred branch when auto-detection is ambiguous. Default: `"main"`.
   - `merge_strategy`: `"squash"` or `"merge"` — controls how worktree branches are merged back. `"squash"` combines all commits into one; `"merge"` preserves individual commits. Default: `"squash"`.

src/resources/extensions/gsd/git-service.ts

@@ -605,11 +605,12 @@ export class GitServiceImpl {
 
   /**
    * Create a snapshot ref for the given label (typically a slice branch name).
-   * Gated on prefs.snapshots === true. Ref path: refs/gsd/snapshots/<label>/<timestamp>
+   * Enabled by default; opt out with prefs.snapshots === false.
+   * Ref path: refs/gsd/snapshots/<label>/<timestamp>
    * The ref points at HEAD, capturing the current commit before destructive operations.
    */
   createSnapshot(label: string): void {
-    if (this.prefs.snapshots !== true) return;
+    if (this.prefs.snapshots === false) return;
 
     const now = new Date();
     const ts = now.getFullYear().toString()
@@ -631,7 +632,7 @@ export class GitServiceImpl {
    * Stub: to be implemented in T03.
    */
   runPreMergeCheck(): PreMergeCheckResult {
-    if (this.prefs.pre_merge_check === false || this.prefs.pre_merge_check === undefined) {
+    if (this.prefs.pre_merge_check === false) {
       return { passed: true, skipped: true };
     }
 

src/resources/extensions/gsd/preferences-types.ts

@@ -33,7 +33,7 @@ export const MODE_DEFAULTS: Record<WorkflowMode, Partial<GSDPreferences>> = {
     git: {
       auto_push: true,
       push_branches: false,
-      pre_merge_check: false,
+      pre_merge_check: "auto",
       merge_strategy: "squash",
       isolation: "none",
     },

src/resources/extensions/gsd/tests/git-service.test.ts

@@ -635,11 +635,11 @@ describe('git-service', async () => {
   // S05: Enhanced features — snapshots, pre-merge checks
   // ═══════════════════════════════════════════════════════════════════════
 
-  // ─── createSnapshot: prefs enabled ─────────────────────────────────────
+  // ─── createSnapshot: default (enabled) ─────────────────────────────────
 
-  test('createSnapshot: enabled', () => {
+  test('createSnapshot: enabled by default when prefs omitted', () => {
     const repo = initBranchTestRepo();
-    const svc = new GitServiceImpl(repo, { snapshots: true });
+    const svc = new GitServiceImpl(repo);
 
     // Create a branch with a commit
     run("git checkout -b gsd/M001/S01", repo);
@@ -675,6 +675,39 @@ describe('git-service', async () => {
     rmSync(repo, { recursive: true, force: true });
   });
 
+  // ─── runPreMergeCheck: default (auto-detect) ──────────────────────────
+
+  test('runPreMergeCheck: auto-detects when prefs omitted', () => {
+    const repo = initBranchTestRepo();
+    createFile(repo, "package.json", JSON.stringify({
+      name: "test-default",
+      scripts: { test: 'node -e "process.exit(0)"' },
+    }));
+    run("git add -A", repo);
+    run('git commit -m "add package.json"', repo);
+
+    // No pre_merge_check pref set — should auto-detect and run
+    const svc = new GitServiceImpl(repo);
+    const result: PreMergeCheckResult = svc.runPreMergeCheck();
+
+    assert.deepStrictEqual(result.passed, true, "runPreMergeCheck auto-detects and passes when prefs omitted");
+    assert.ok(!result.skipped, "runPreMergeCheck is not skipped when prefs omitted and package.json exists");
+
+    rmSync(repo, { recursive: true, force: true });
+  });
+
+  test('runPreMergeCheck: gracefully skips when prefs omitted and no package.json', () => {
+    const repo = initBranchTestRepo();
+    // No package.json — auto-detect should skip gracefully
+    const svc = new GitServiceImpl(repo);
+    const result: PreMergeCheckResult = svc.runPreMergeCheck();
+
+    assert.deepStrictEqual(result.passed, true, "runPreMergeCheck passes when no package.json (skip)");
+    assert.deepStrictEqual(result.skipped, true, "runPreMergeCheck skips when no test runner detected");
+
+    rmSync(repo, { recursive: true, force: true });
+  });
+
   // ─── runPreMergeCheck: pass ────────────────────────────────────────────
 
   test('runPreMergeCheck: pass', () => {

src/resources/extensions/gsd/tests/preferences.test.ts

@@ -59,7 +59,7 @@ test("solo mode applies correct defaults", () => {
   const result = applyModeDefaults("solo", { mode: "solo" });
   assert.equal(result.git?.auto_push, true);
   assert.equal(result.git?.push_branches, false);
-  assert.equal(result.git?.pre_merge_check, false);
+  assert.equal(result.git?.pre_merge_check, "auto");
   assert.equal(result.git?.merge_strategy, "squash");
   assert.equal(result.git?.isolation, "none");
   assert.equal(result.unique_milestone_ids, false);