#1091 Anchor a project-deployed link where its target deploys

[williamthorsen]

What

Fixes an issue where cross-references between guidance files that sync deploys into a project worked only if the linked guidance was also installed in the user's home directory, silently degrading agent output for anyone else.

Why

Guidance deployed into a project pointed at files that exist only in the user's home harness directory. A skill's cross-reference to a sibling resolved only when that sibling happened to also be installed globally; otherwise it named a path nothing creates. A dead reference of this kind never surfaces as an error, because the agent reading it improvises past the missing target.

Details

🐛 Bug fixes

• The constant path prefix threaded through every Markdown link rewrite is replaced by an injected anchor, so a target's emitted absolute path is decided by the tree that actually deploys it. createSkillLinkAnchor places a skill directory the run writes under the deploying domain's base and everything else under the harness home; createContentRootLinkAnchor delegates to it for targets under skills/ and keeps the harness home otherwise.
• The set of deployed skill directories is derived from the run's own output — declared skill slugs filtered per harness, unioned with the rulebook-delivered skill names — rather than from source layout, so the anchor names precisely the directories the run creates.
• A link to a skill the run does not deploy stays anchored at the harness home, its only addressable location; re-pointing it into the project would make it unresolvable outright.
• Home-domain output is unchanged by construction: sync --global sets the domain base to ~, which collapses the anchor's two branches to the same string.
• install and content validation keep their existing behavior through a homeAnchor constructor that reproduces the single anchor every caller had before.
• The rulebook render context is threaded as a closure rather than rebuilt per call site, so the pre-write gate and the delivery passes it guards cannot disagree about where a link target lands.

🧪 Tests

• Unit coverage for both anchor constructors across all four target shapes in both domains, including a table-driven case pinning the home-domain identity property directly.
• End-to-end sync coverage for each artifact type — declared skill, rulebook body, and subagent — in the project domain, plus the negative case for a target the run does not deploy and a sync --global case pinning the home-domain anchor.

📚 Documentation

• The rulebook authoring guidance states which root a link target carries in each domain, with a delivered-skill example beside the existing support-entry one.
• The partials reference scopes the project-root exception to bare sync.

Closes #1091

[github-actions]

Dependency audit

Production dependency audit passed.