fix(attribution): submodule leak, PR body nesting, shallow-clone bail, schema default

- attachCommitAttribution: when HEAD didn't move in our cwd, leave
  pending attributions alone instead of dropping them. The case can be
  a failed commit, `git reset HEAD~1`, OR `cd submodule && git commit`
  (inner repo's HEAD moves, ours doesn't). Dropping was overly
  aggressive and silently lost outer-repo edits in the submodule case.
- addAttributionToPR: mirror addCoAuthorToGitCommit's nested-match
  rejection so `gh pr create --body "docs mention -b 'flag'"` picks the
  outer `--body`, not the inner literal `-b`. Splicing into the inner
  match would corrupt the body. Regression test added.
- getCommittedFileInfo: when `rev-parse --verify HEAD~1` fails, also
  check `rev-list --count HEAD === 1` to confirm HEAD is the true
  root commit. In a shallow clone, HEAD~1 is unreadable but the commit
  has a parent recorded — falling back to `diff-tree --root` would
  diff against the empty tree and over-attribute the entire commit.
  Bail with a debug warning instead.
- generate-settings-schema: lift `default` (and `description`) out of
  the inner `anyOf[N]` schema to the outer level when wrapping with
  `legacyTypes`. Most JSON-schema-driven editors only surface
  top-level defaults; burying the default under `anyOf` lost the
  "enabled by default" hint. Also extend the default filter to
  publish non-empty plain objects (so `gitCoAuthor`'s default can
  appear). gitCoAuthor's source default updated to the runtime shape
  `{commit: true, pr: true}` to match `normalizeGitCoAuthor`.

scripts/generate-settings-schema.ts

@@ -148,7 +148,7 @@ function convertSettingToJsonSchema(
       break;
   }
 
-  // Add default value for simple types only
+  // Add default value for simple and object types
   if (setting.default !== undefined && setting.default !== null) {
     const defaultVal = setting.default;
     if (
@@ -159,6 +159,14 @@ function convertSettingToJsonSchema(
       schema.default = defaultVal;
     } else if (Array.isArray(defaultVal) && defaultVal.length > 0) {
       schema.default = defaultVal;
+    } else if (
+      typeof defaultVal === 'object' &&
+      !Array.isArray(defaultVal) &&
+      Object.keys(defaultVal).length > 0
+    ) {
+      // Non-empty plain object — publish so IDE editors can surface the
+      // default value (e.g. `{commit: true, pr: true}` for gitCoAuthor).
+      schema.default = defaultVal;
     }
   }
 
@@ -166,11 +174,20 @@ function convertSettingToJsonSchema(
   // later expanded into an object), wrap with `anyOf` so existing values
   // in users' settings.json don't trip the IDE schema validator while
   // they wait for our migration to rewrite them on the next launch.
+  //
+  // Lift `description` and `default` to the outer (anyOf) level so IDE
+  // editors that surface schema-driven defaults / descriptions still see
+  // them — burying these behind `anyOf[N]` makes most validators ignore
+  // the `default`, which loses the "enabled by default" hint for any
+  // setting using `legacyTypes`.
   if (setting.legacyTypes && setting.legacyTypes.length > 0) {
     const description = schema.description;
+    const defaultVal = schema.default;
     delete schema.description;
+    delete schema.default;
     return {
       ...(description ? { description } : {}),
+      ...(defaultVal !== undefined ? { default: defaultVal } : {}),
       anyOf: [...setting.legacyTypes.map((t) => ({ type: t })), schema],
     };
   }