fix(#813): apply per-runtime skill path rewrites in applySurface (#817)

* fix(#813): apply per-runtime skill path rewrites in applySurface

applySurface() re-staged skill artifacts but, unlike installRuntimeArtifacts(),
never applied the per-runtime path rewrites. So /gsd:surface
(profile/enable/disable/reset) overwrote installed SKILL.md bodies with the
converter's default ~/.claude paths instead of the install target (pathPrefix),
silently regressing skill path references for every skillsKind runtime until
the next reinstall.

applySurface now mirrors installRuntimeArtifacts: for kind.kind === 'skills' it
derives pathPrefix the same way and applies applyRuntimeContentRewritesInPlace
on the staged dir before syncing.

- bin/install.js: export applyRuntimeContentRewritesInPlace
- runtime-artifact-layout.cts: carry resolved scope on Layout; export
  getInstallExports; type computePathPrefix/applyRuntimeContentRewritesInPlace
  on InstallExports
- surface.cts: lazily derive pathPrefix (only when a skills kind exists) and
  apply the rewrite via the shared getInstallExports accessor — single source of
  truth with install, only skills kinds rewritten (matches install)
- tests: regression test parameterized over cursor + codex asserting
  post-applySurface bodies carry the install pathPrefix, not ~/.claude
- CONTEXT.md: glossary updated for the applySurface rewrite parity + scope seam

Closes #813

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#813): add changeset fragment for PR #817

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* test(#813): normalize configDir prefix to forward slashes for Windows CI

The #813 regression assertion compared skill bodies against a raw
${configDir}/ prefix, but production derives pathPrefix via
path.resolve(configDir).replace(/\\/g, '/'). On Windows, mkdtempSync
returns backslash paths while the rewritten body uses forward slashes,
so the assertion would fail Windows-only (not covered by local gsd-test).
Normalize the expected prefix the same way production does.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

CONTEXT.md

@@ -116,7 +116,7 @@ Module owning install detection for `/gsd:update`. `resolveUpdateContext({ home,
 Module owning which skills and agents are written to runtime config directories at install time (Phase 1) and at runtime via cluster-level toggles (Phase 2). Phase 1: `gsd-core/bin/lib/install-profiles.cjs` defines named profiles (`core`, `standard`, `full`), computes transitive closure over `requires:` frontmatter, stages skills/agents to runtime config dirs, and persists the chosen profile in a `.gsd-profile` marker. Profile resolution precedence: explicit `--profile=` flag > `.gsd-profile` marker > `full`. `--minimal`/`--core-only` are back-compat aliases for `--profile=core`. Phase 2: `gsd-core/bin/lib/surface.cjs` implements the `/gsd:surface` slash command for cluster-level enable/disable without reinstall; cluster definitions live in `gsd-core/bin/lib/clusters.cjs`; per-runtime state persists in `<runtimeConfigDir>/.gsd-surface.json` independent from the `.gsd-profile` marker. See ADR-0011.
 
 ### Runtime Artifact Layout Module
-Module owning the per-runtime mapping from artifact kind to filesystem placement. ADR-3660 defines the typed `kinds` per runtime (`commands`, `agents`, `skills`) with destination subpath, prefix, and stage adapter (with per-runtime converters in `bin/install.js`: `convertClaudeCommandToClaudeSkill`, `…CodexSkill`, `…CopilotSkill`, `…AntigravitySkill`). Phase 1 applies this seam to the Runtime Surface Module (`surface.cjs:applySurface`). Phase 2 is planned to migrate install/uninstall in `bin/install.js` so all lifecycle sites iterate one shared layout table instead of re-encoding runtime layout logic. This design is intended to remove the #3659 class of omissions. Migrations remain under the Installer Migration Module (ADR-0008). See ADR-3660.
+Module owning the per-runtime mapping from artifact kind to filesystem placement. ADR-3660 defines the typed `kinds` per runtime (`commands`, `agents`, `skills`) with destination subpath, prefix, and stage adapter (with per-runtime converters in `bin/install.js`: `convertClaudeCommandToClaudeSkill`, `…CodexSkill`, `…CopilotSkill`, `…AntigravitySkill`). Phase 1 applies this seam to the Runtime Surface Module (`surface.cjs:applySurface`); as of #813, `applySurface` applies the same per-runtime skill-body path rewrites as `installRuntimeArtifacts` for `skills` kinds — re-surfacing no longer overwrites installed SKILL.md bodies with converter-default `~/.claude` paths. The shared accessor `getInstallExports` (exported from `runtime-artifact-layout.cjs`) is the single-source seam through which `surface.cjs` reaches `computePathPrefix` and `applyRuntimeContentRewritesInPlace`; the resolved `scope` (`'local'`|`'global'`) is now carried on the `Layout` object returned by `resolveRuntimeArtifactLayout` so `applySurface` derives the same `pathPrefix` (global `$HOME` form vs. absolute) as a fresh install. Phase 2 is planned to migrate install/uninstall in `bin/install.js` so all lifecycle sites iterate one shared layout table instead of re-encoding runtime layout logic. This design is intended to remove the #3659 class of omissions. Migrations remain under the Installer Migration Module (ADR-0008). See ADR-3660.
 
 ### Runtime Install Policy Module
 Projects a pure, typed install plan for a given runtime by composing artifact placements (Runtime Artifact Layout Module), command text (Shell Command Projection Module), and per-runtime config intentions — with no filesystem IO or format-specific serialization. Runtime-specific adapters consume the plan and execute concrete file mutations and config rendering. See ADR-58.