#512 deleted `src/agents/` when the AI surface went skills-only, but seven
maintainer docs kept printing `src/agents/*.agent.ts` in their tree
diagrams and registration tables. `code_examples.md` was the worst of it:
after registering a skill it told the author to "add its name to an agent
in `src/agents/*.agent.ts`" — an instruction that cannot be followed.
`src/cubes/` had the same shape, dropped in favour of datasets (ADR-0021,
noted in objectstack.config.ts) and still drawn in two trees.

Nothing checked, because a path in prose is just prose. That is the same
failure mode as #493 one layer out: metadata validation sees a
well-formed string and stops, so the reference rots silently and the next
reader — human or agent — is sent somewhere that does not exist.

- README.md, AGENTS.md, docs/README.md, docs/STATUS.md,
  docs/ARCHITECTURE.md, docs/developers/code_examples.md: drop the agent
  and cube directories; README picks up `src/datasets/` (the layer that
  actually replaced cubes) and its flow count goes 20 → 23; AGENTS.md's
  `*.action.ts` becomes `*.actions.ts`, the real suffix.
- code_examples.md: drop the skill `permissions: [...]` key — SkillSchema
  has no such field and strips it silently (#511) — and fill the gap the
  deletions leave. The example now says which two sources a `tools` name
  can resolve to (platform data tools, or `action_<name>` from an
  `ai.exposed` Action with a headless path), why `defineTool` is not a
  third one, that reasoning belongs in `instructions` (ADR-0109), and
  where the guard lives.
- ARCHITECTURE.md: same note, plus the `case_triage` skill its table had
  been missing.

Adds a repo-tree guard to test/docs-drift.test.ts — every `src/<dir>/` a
maintainer doc names must resolve on disk, with `docs/archive/` excluded
as a historical record. It earned its place immediately by failing on a
stray `no src/agents/` parenthetical in this change's own first pass.

155 tests (+9), typecheck, validate and build pass; the 2 remaining
validate warnings are the pre-existing campaign_enrollment ones.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y9STuduWbrAwcgviziaV4e