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/SKILL.md.tmpl

@@ -14,7 +14,7 @@ allowed-tools:
   - AskUserQuestion
 ---
 
-{{UPDATE_CHECK}}
+{{PREAMBLE}}
 
 # Pre-Landing PR Review
 
@@ -64,9 +64,11 @@ Run `git diff origin/main` to get the full diff. This includes both committed an
 
 Apply the checklist against the diff in two passes:
 
-1. **Pass 1 (CRITICAL):** SQL & Data Safety, LLM Output Trust Boundary
+1. **Pass 1 (CRITICAL):** SQL & Data Safety, Race Conditions & Concurrency, LLM Output Trust Boundary, Enum & Value Completeness
 2. **Pass 2 (INFORMATIONAL):** Conditional Side Effects, Magic Numbers & String Coupling, Dead Code & Consistency, LLM Prompt Issues, Test Gaps, View/Frontend
 
+**Enum & Value Completeness requires reading code OUTSIDE the diff.** When the diff introduces a new enum value, status, tier, or type constant, use Grep to find all files that reference sibling values, then Read those files to check if the new value is handled. This is the one category where within-diff review is insufficient.
+
 Follow the output format specified in the checklist. Respect the suppressions — do NOT flag items listed in the "DO NOT flag" section.
 
 ---
@@ -75,7 +77,7 @@ Follow the output format specified in the checklist. Respect the suppressions
 
 **Always output ALL findings** — both critical and informational. The user must see every issue.
 
-- If CRITICAL issues found: output all findings, then for EACH critical issue use a separate AskUserQuestion with the problem, your recommended fix, and options (A: Fix it now, B: Acknowledge, C: False positive — skip).
+- If CRITICAL issues found: output all findings, then for EACH critical issue use a separate AskUserQuestion with the problem, then `RECOMMENDATION: Choose A because [one-line reason]`, then options (A: Fix it now, B: Acknowledge, C: False positive — skip).
   After all critical questions are answered, output a summary of what the user chose for each issue. If the user chose A (fix) on any issue, apply the recommended fixes. If only B/C were chosen, no action needed.
 - If only non-critical issues found: output findings. No further action needed.
 - If no issues found: output `Pre-Landing Review: No issues found.`