docs: update project documentation for v1.73.0.0

- README.md, docs/skills.md, AGENTS.md: /autoplan phase order corrected to
  CEO → design → DX → eng (eng always last); /review rows note the advisory
  simplification lens
- docs/PROJECT_STRUCTURE.md: add agents-digest/, gen-agents-digest.ts,
  sandbox-doctor.sh, test-free-shards.ts to the annotated tree
- CONTRIBUTING.md: document GSTACK_FREE_JOBS, GSTACK_FREE_RETRY_FLAKY, and
  the sandbox-doctor one-command fixer in the Tier 1 test section

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -201,7 +201,7 @@ Each skill feeds into the next. `/office-hours` writes a design doc that `/plan-
 | `/plan-design-review` | **Senior Designer** | Rates each design dimension 0-10, explains what a 10 looks like, then edits the plan to get there. AI Slop detection. Interactive — one AskUserQuestion per design choice. |
 | `/plan-devex-review` | **Developer Experience Lead** | Interactive DX review: explores developer personas, benchmarks against competitors' TTHW, designs your magical moment, traces friction points step by step. Three modes: DX EXPANSION, DX POLISH, DX TRIAGE. 20-45 forcing questions. |
 | `/design-consultation` | **Design Partner** | Build a complete design system from scratch. Researches the landscape, proposes creative risks, generates realistic product mockups. |
-| `/review` | **Staff Engineer** | Find the bugs that pass CI but blow up in production. Auto-fixes the obvious ones. Flags completeness gaps. |
+| `/review` | **Staff Engineer** | Find the bugs that pass CI but blow up in production. Auto-fixes the obvious ones. Flags completeness gaps. Advisory simplification lens flags over-built code — never blocks, never auto-applies. |
 | `/investigate` | **Debugger** | Systematic root-cause debugging. Iron Law: no fixes without investigation. Traces data flow, tests hypotheses, stops after 3 failed fixes. |
 | `/design-review` | **Designer Who Codes** | Same audit as /plan-design-review, then fixes what it finds. Atomic commits, before/after screenshots. |
 | `/devex-review` | **DX Tester** | Live developer experience audit. Actually tests your onboarding: navigates docs, tries the getting started flow, times TTHW, screenshots errors. Compares against `/plan-devex-review` scores — the boomerang that shows if your plan matched reality. |
@@ -220,7 +220,7 @@ Each skill feeds into the next. `/office-hours` writes a design doc that `/plan-
 | `/retro` | **Eng Manager** | Team-aware weekly retro. Per-person breakdowns, shipping streaks, test health trends, growth opportunities. `/retro global` runs across all your projects and AI tools (Claude Code, Codex, Gemini). |
 | `/browse` | **QA Engineer** | Give the agent eyes. Real Chromium browser, real clicks, real screenshots. ~100ms per command. `/open-gstack-browser` launches GStack Browser with sidebar, anti-bot stealth, and auto model routing. |
 | `/setup-browser-cookies` | **Session Manager** | Import cookies from your real browser (Chrome, Arc, Brave, Edge) into the headless session. Test authenticated pages. |
-| `/autoplan` | **Review Pipeline** | One command, fully reviewed plan. Runs CEO → design → eng review automatically with encoded decision principles. Surfaces only taste decisions for your approval. |
+| `/autoplan` | **Review Pipeline** | One command, fully reviewed plan. Runs CEO → design → DX → eng review automatically (eng always last, so the shipping gate reviews the final amended plan) with encoded decision principles. Surfaces only taste decisions for your approval. |
 | `/spec` | **Spec Author** | Turn vague intent into a precise, executable spec in five phases (why, scope, technical with mandatory code-reading, draft, file). Codex quality gate before file (blocks below 7/10), fail-closed secret redaction, dedupe against existing issues, archive to `$GSTACK_STATE_ROOT/projects/$SLUG/specs/` for team-corpus recall. `--execute` spawns `claude -p` in a fresh worktree; `/ship` auto-closes the source issue on merge. Plan-mode aware. |
 | `/learn` | **Memory** | Manage what gstack learned across sessions. Review, search, prune, and export project-specific patterns, pitfalls, and preferences. Learnings compound across sessions so gstack gets smarter on your codebase over time. |
 | `/make-pdf` | **Publisher** | Markdown in, publication-quality document out. Mermaid and excalidraw fences render as vector diagrams, fully offline. Images scale to the page and never truncate; wide diagrams get their own landscape page. `--to html` emits one self-contained file, `--to docx` a Word doc. |
@@ -233,7 +233,7 @@ Each skill feeds into the next. `/office-hours` writes a design doc that `/plan-
 | **End users** (UI, web app, mobile) | `/plan-design-review` | `/design-review` |
 | **Developers** (API, CLI, SDK, docs) | `/plan-devex-review` | `/devex-review` |
 | **Architecture** (data flow, perf, tests) | `/plan-eng-review` | `/review` |
-| **All of the above** | `/autoplan` (runs CEO → design → eng → DX, auto-detects which apply) | — |
+| **All of the above** | `/autoplan` (runs CEO → design → DX → eng, auto-detects which apply; eng always last) | — |
 
 ### Power tools