docs(wiki): update project wiki

[fro-bot]

Weekly wiki refresh. The lint pass found no broken wikilinks and no orphan pages; seven of the eight pages were stale against their sources frontmatter and were updated in place. No unchanged page was regenerated.

What changed and why

The last three weeks of work clustered into two stories, and most of this diff is those two stories being written down.

Session persistence stopped reporting a boolean. saveCache now returns a CacheSaveResult with two independent persistence axes plus a named outcome, and the CACHE_SAVED state key that crosses into the post-action hook carries a four-value enum instead of true/false. [[Session Persistence]] gained a section on what a save actually reports — including the explicit caveat that cache-rejected covers several causes because the @actions/cache boundary cannot distinguish them, not because one was diagnosed. [[Execution Lifecycle]] gained a section on the cleanup-to-post handoff, covering why CLEANUP_METADATA_WRITTEN had to exist separately (CACHE_SAVED is seeded before cleanup runs, so not-persisted is ambiguous between "cleanup ran and was denied" and "cleanup never ran"). Also documented: save keys are now scoped by run attempt, because re-runs were colliding with the first attempt's immutable cache entry and having their state discarded through the "already exists" success path.

Setup grew a real distinction between an install directory and an executable. Four fixes in five days traced back to the same conflation, so [[Setup and Configuration]] now describes it as one story rather than four bullet points — plus the new fail-fast platform gate (which replaced silent fallbacks that mapped an unsupported arch onto the x64 asset and downloaded a binary that could not execute), the corrected plugin-install condition, and the two new diagnostics that accompany a failed plugin install.

Smaller updates

• [[Prompt Architecture]] — documents the ResponseSurface axis, which was undocumented. Covers why pr-review-permitted exists (a PR mention is legitimately either a review request or a question) and why the policy table is pinned with satisfies.
• [[Conventions and Patterns]] — new section naming the "named outcomes over booleans" pattern, since it now has enough instances to be a convention rather than a one-off.
• [[Architecture Overview]], Troubleshooting — module map entries, and a new setup-failures section keyed to the error strings an operator would actually see.
• index.md — summary sync.

Verification

Re-ran the lint pass after editing: wikilinks resolve, no orphans, in-page anchors resolve, relative paths exist, every sources entry exists on disk, and every index row matches its page's frontmatter type and summary.

Scope is docs/wiki/ only — no source files, no AGENTS.md.

Run Summary

• Trigger: schedule (thread schedule-d7190410-34062354146)
• Run: 34062354146
• Baseline: d9a88dee (last docs(wiki): commit), 46 commits reviewed
• Pages updated: 7 of 8 + index; 0 created, 0 deleted
• Lint: clean (0 broken links, 0 orphans, 0 missing sources)