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>

CLAUDE.md

@@ -72,6 +72,35 @@ When you need to interact with a browser (QA, dogfooding, cookie setup), use the
 `mcp__claude-in-chrome__*` tools — they are slow, unreliable, and not what this
 project uses.
 
+## Vendored symlink awareness
+
+When developing gstack, `.claude/skills/gstack` may be a symlink back to this
+working directory (gitignored). This means skill changes are **live immediately** —
+great for rapid iteration, risky during big refactors where half-written skills
+could break other Claude Code sessions using gstack concurrently.
+
+**Check once per session:** Run `ls -la .claude/skills/gstack` to see if it's a
+symlink or a real copy. If it's a symlink to your working directory, be aware that:
+- Template changes + `bun run gen:skill-docs` immediately affect all gstack invocations
+- Breaking changes to SKILL.md.tmpl files can break concurrent gstack sessions
+- During large refactors, remove the symlink (`rm .claude/skills/gstack`) so the
+  global install at `~/.claude/skills/gstack/` is used instead
+
+**For plan reviews:** When reviewing plans that modify skill templates or the
+gen-skill-docs pipeline, consider whether the changes should be tested in isolation
+before going live (especially if the user is actively using gstack in other windows).
+
+## CHANGELOG style
+
+CHANGELOG.md is **for users**, not contributors. Write it like product release notes:
+
+- Lead with what the user can now **do** that they couldn't before. Sell the feature.
+- Use plain language, not implementation details. "You can now..." not "Refactored the..."
+- Put contributor/internal changes in a separate "For contributors" section at the bottom.
+- Every entry should make someone think "oh nice, I want to try that."
+- No jargon: say "every question now tells you which project and branch you're in" not
+  "AskUserQuestion format standardized across skill templates via preamble resolver."
+
 ## Deploying to the active skill
 
 The active skill lives at `~/.claude/skills/gstack/`. After making changes: