feat: contributor mode, session awareness, recommendation format (#90)

* feat: contributor mode, session awareness, universal RECOMMENDATION format

- Rename {{UPDATE_CHECK}} → {{PREAMBLE}} across all 10 skill templates
- Add session tracking (touch ~/.gstack/sessions/$PPID, count active sessions)
- ELI16 mode when 3+ concurrent sessions detected (re-ground user on context)
- Contributor mode: auto-file field reports to ~/.gstack/contributor-logs/
- Universal AskUserQuestion format: context → question → RECOMMENDATION → options
- Update plan-ceo-review and plan-eng-review to reference preamble baseline
- Add vendored symlink awareness section to CLAUDE.md
- Rewrite CONTRIBUTING.md with contributor workflow and cross-project testing
- Add tests for contributor mode and session awareness in generated output
- Add E2E eval for contributor mode report filing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add Enum & Value Completeness to /review critical checklist

New CRITICAL review category that traces new enum values, status strings,
and type constants through every consumer outside the diff. Catches the
class of bugs where a new value is added but not handled in all switch/case
chains, allowlists, or frontend-backend contracts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: bump v0.4.1, user-facing changelog, update qa-only template and architecture docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add CHANGELOG style guide — user-facing, sell the feature

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: rewrite v0.4.1 changelog to be user-facing and sell the features

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add evals for RECOMMENDATION format, session awareness, and enum completeness

Free tests (Tier 1): RECOMMENDATION format + session awareness in all
preamble SKILL.md files, enum completeness checklist structure and CRITICAL
classification.

E2E eval: /review catches missed enum handlers when a new status value
is added but not handled in case/switch and notify methods.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add E2E eval for session awareness ELI16 mode

Stubs _SESSIONS=4, gives agent a decision point on feature/add-payments
branch, verifies the output re-grounds the user with project, branch,
context, and RECOMMENDATION — the ELI16 mode behavior for 3+ sessions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: contributor mode eval marked FAIL due to expected browse error

The test intentionally runs a nonexistent binary to trigger contributor
mode. The session runner's browse error detection catches "no such file
or directory...browse" and sets browseErrors, causing recordE2E to mark
passed=false. Override passed to check only exitReason since the browse
error is the expected scenario.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

review/checklist.md

@@ -48,6 +48,13 @@ Be terse. For each issue: one line describing the problem, one line with the fix
 - LLM-generated values (emails, URLs, names) written to DB or passed to mailers without format validation. Add lightweight guards (`EMAIL_REGEXP`, `URI.parse`, `.strip`) before persisting.
 - Structured tool output (arrays, hashes) accepted without type/shape checks before database writes.
 
+#### Enum & Value Completeness
+When the diff introduces a new enum value, status string, tier name, or type constant:
+- **Trace it through every consumer.** Read (don't just grep — READ) each file that switches on, filters by, or displays that value. If any consumer doesn't handle the new value, flag it. Common miss: adding a value to the frontend dropdown but the backend model/compute method doesn't persist it.
+- **Check allowlists/filter arrays.** Search for arrays or `%w[]` lists containing sibling values (e.g., if adding "revise" to tiers, find every `%w[quick lfg mega]` and verify "revise" is included where needed).
+- **Check `case`/`if-elsif` chains.** If existing code branches on the enum, does the new value fall through to a wrong default?
+To do this: use Grep to find all references to the sibling values (e.g., grep for "lfg" or "mega" to find all tier consumers). Read each match. This step requires reading code OUTSIDE the diff.
+
 ### Pass 2 — INFORMATIONAL
 
 #### Conditional Side Effects
@@ -101,8 +108,8 @@ Be terse. For each issue: one line describing the problem, one line with the fix
 CRITICAL (blocks /ship):          INFORMATIONAL (in PR body):
 ├─ SQL & Data Safety              ├─ Conditional Side Effects
 ├─ Race Conditions & Concurrency  ├─ Magic Numbers & String Coupling
-└─ LLM Output Trust Boundary      ├─ Dead Code & Consistency
-                                   ├─ LLM Prompt Issues
+├─ LLM Output Trust Boundary      ├─ Dead Code & Consistency
+└─ Enum & Value Completeness      ├─ LLM Prompt Issues
                                    ├─ Test Gaps
                                    ├─ Crypto & Entropy
                                    ├─ Time Window Safety