refactor: split preamble.ts into submodules (byte-identical output)

Splits scripts/resolvers/preamble.ts (841 lines, 18 generator functions +
composition root) into one file per generator under
scripts/resolvers/preamble/. Root preamble.ts becomes a thin composition
layer (~80 lines of imports + generatePreamble).

Before:
  scripts/resolvers/preamble.ts  841 lines

After:
  scripts/resolvers/preamble.ts                                   83 lines
  scripts/resolvers/preamble/generate-preamble-bash.ts            97 lines
  scripts/resolvers/preamble/generate-upgrade-check.ts            48 lines
  scripts/resolvers/preamble/generate-lake-intro.ts               16 lines
  scripts/resolvers/preamble/generate-telemetry-prompt.ts         37 lines
  scripts/resolvers/preamble/generate-proactive-prompt.ts         25 lines
  scripts/resolvers/preamble/generate-routing-injection.ts        49 lines
  scripts/resolvers/preamble/generate-vendoring-deprecation.ts    36 lines
  scripts/resolvers/preamble/generate-spawned-session-check.ts    11 lines
  scripts/resolvers/preamble/generate-ask-user-format.ts          16 lines
  scripts/resolvers/preamble/generate-completeness-section.ts     19 lines
  scripts/resolvers/preamble/generate-repo-mode-section.ts        12 lines
  scripts/resolvers/preamble/generate-test-failure-triage.ts     108 lines
  scripts/resolvers/preamble/generate-search-before-building.ts   14 lines
  scripts/resolvers/preamble/generate-completion-status.ts       161 lines
  scripts/resolvers/preamble/generate-voice-directive.ts          60 lines
  scripts/resolvers/preamble/generate-context-recovery.ts         51 lines
  scripts/resolvers/preamble/generate-continuous-checkpoint.ts    48 lines
  scripts/resolvers/preamble/generate-context-health.ts           31 lines

Byte-identity verification (the real gate per Codex correction):
- Before refactor: snapshotted 135 generated SKILL.md files via
  `find -name SKILL.md -type f | grep -v /gstack/` across all hosts.
- After refactor: regenerated with `bun run gen:skill-docs --host all`
  and re-snapshotted.
- `diff -r baseline after` returned zero differences and exit 0.

The `--host all --dry-run` gate passes too. No template or host behavior
changes — purely a code-organization refactor.

Test fix: audit-compliance.test.ts's telemetry check previously grepped
preamble.ts directly for `_TEL != "off"`. After the refactor that logic
lives in preamble/generate-preamble-bash.ts. Test now concatenates all
preamble submodule sources before asserting — tracks the semantic contract,
not the file layout. Doing the minimum rewrite preserves the test's intent
(conditional telemetry) without coupling it to file boundaries.

Why now: we were in-session with full context. Codex had downgraded this
from mandatory to optional, but the preamble had grown to 841 lines and
was getting harder to navigate. User asked "why not?" given the context
was hot. Shipping it as a clean bisectable commit while all the prior
preamble.ts changes are fresh reduces rebase pain later.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/audit-compliance.test.ts

@@ -33,7 +33,16 @@ describe('Audit compliance', () => {
 
   // Fix 2: Conditional telemetry — binary calls wrapped with existence check
   test('preamble telemetry calls are conditional on _TEL and binary existence', () => {
-    const preamble = readFileSync(join(ROOT, 'scripts/resolvers/preamble.ts'), 'utf-8');
+    // After the preamble.ts refactor (Item 9), the bash/telemetry logic lives
+    // in submodules under scripts/resolvers/preamble/. Concatenate all preamble
+    // source (root + submodules) and assert against the combined text so this
+    // test tracks the semantic contract, not the file layout.
+    const preambleDir = join(ROOT, 'scripts/resolvers/preamble');
+    const submoduleFiles = existsSync(preambleDir)
+      ? readdirSync(preambleDir).filter(f => f.endsWith('.ts')).map(f => readFileSync(join(preambleDir, f), 'utf-8'))
+      : [];
+    const rootPreamble = readFileSync(join(ROOT, 'scripts/resolvers/preamble.ts'), 'utf-8');
+    const preamble = [rootPreamble, ...submoduleFiles].join('\n');
     // Pending finalization must check _TEL and binary existence
     expect(preamble).toContain('_TEL" != "off"');
     expect(preamble).toContain('-x ');