msd-core/docs/adr/1508-runtime-artifact-conversion-module.md

Runtime Artifact Conversion Module owns per-runtime content rewriting

• Status: Accepted
• Date: 2026-06-20
• Issue: #1508
• Epic: #1507
• Implementation: Phase 1 (helper relocation, no behavior change) → Phase 2 (engine move + relay deletion)

The Runtime Surface Module (src/surface.cts → surface.cjs) re-materializes a resolved skill surface to disk via applySurface. For skills kinds it must rewrite staged SKILL.md bodies so their @-ref paths point at the install target (pathPrefix) instead of the converter's default ~/.claude paths (#813). To do that it reaches up into the 12,289-line hand-authored bin/install.js via getInstallExports() (src/runtime-artifact-layout.cts:53-69) — a lazy require('../../../bin/install.js') guarded by a save/set/restore of GSD_TEST_MODE — to borrow computePathPrefix and applyRuntimeContentRewritesInPlace.

This is the last upward dependency from the .cts source tree into the hand-authored installer. It forces an env-var dance at a test seam, and it leaks: applySurface (and bin/install.js's own three call sites) each re-derive the same five path-prefix inputs (scope→isGlobal, runtime==='opencode', process.platform, normalized resolvedTarget, normalized homeDir) before calling computePathPrefix. The prefix-derivation knowledge is duplicated across surface.cts and install.js.

CONTEXT.md already names the Runtime Artifact Conversion Module (src/runtime-artifact-conversion.cts) as the [Planned] sibling of the Layout Module — placement vs. content. ADR-3660 §Initial Scope deferred exactly this consolidation: "A future ADR may consolidate them into a Skill Conversion Module if a second consumer emerges." surface.cts is that second consumer. This is that future ADR.

Decision

• Promote the [Planned] Runtime Artifact Conversion Module (src/runtime-artifact-conversion.cts) to the single owner of per-runtime content rewriting: the per-runtime converters (already relocated as ADR-3660's "first slice", #1099), plus the rewrite engine _applyRuntimeRewrites, the staged-content walkers, path-prefix derivation, and commit attribution. The Runtime Artifact Layout Module keeps owning placement only.
• Public seam — two deep calls; the caller passes only what it has, the module derives the rest:
  • rewriteStagedSkillBodies(stagedDir, { runtime, configDir, scope }, env?) — in-place walk (skills / kimi-agents).
  • rewriteStagedCommandBodies(stagedDir, { runtime, configDir, scope }, env?) → tempDir — copy-to-temp (commands).
  • The module internally derives isGlobal/isOpencode/isWindowsHost/resolvedTarget/homeDir and the path prefix. env = { homedir = os.homedir, platform = process.platform } = {} is an injected test seam (the clock-seam analog, RULESET.TESTS.clock-seam).
• computePathPrefix becomes private to the module, exported as _computePathPrefix for direct unit + fast-check property tests (RULESET.TESTS.property-based-testing). The hand-reimplemented copy in tests/path-replacement.test.cjs is deleted so the real function is what's tested (it is effectively untested today).
• Dependency direction: bin/install.js and runtime-artifact-layout.cts import the conversion module; the conversion module imports nothing upward (not install.js, not layout) — only deeper leaves.
• getDirName(runtime) relocates to src/runtime-name-policy.cts (a clean fs/path-only leaf), so the conversion module can consume it without dragging in capability-registry.cjs (which runtime-homes.cjs requires). processAttribution / getCommitAttribution move into the conversion module (attribution is content transformation).
• The duplicate convertClaudeToAugmentMarkdown (verified byte-identical in install.js:2584 and conversion.cts:976) collapses to the conversion-module copy; install.js's local copy is deleted (it already re-exports ...runtimeArtifactConversion).
• getInstallExports / loadInstallExports / the InstallExports interface and the GSD_TEST_MODE require of bin/install.js are deleted from runtime-artifact-layout.cts. surface.cts (the sole consumer) calls the conversion module's deep functions directly — removing the last upward .cts → install.js dependency.

Initial Scope

Phase 1 — helper relocation (no behavior change)

1. Move getDirName → runtime-name-policy.cts; re-point its 13 install.js call sites.
2. Move processAttribution + getCommitAttribution → conversion.cts; re-point their 21 install.js call sites.
3. Delete install.js's local convertClaudeToAugmentMarkdown (copies confirmed byte-identical); rely on the conversion-module copy via the existing ...runtimeArtifactConversion export spread. Add a characterization test snapshotting current augment skills-rewrite output as insurance — it should pass unchanged.
4. No public-interface change; install.js and surface.cts behavior unchanged.

Phase 2 — engine move + deepen + delete relay

1. Move _applyRuntimeRewrites, applyRuntimeContentRewritesInPlace, applyRuntimeContentRewritesForCommandsInPlace, and computePathPrefix into conversion.cts.
2. Expose rewriteStagedSkillBodies / rewriteStagedCommandBodies; privatize computePathPrefix (_computePathPrefix for tests).
3. surface.cts:applySurface and install.js's three internal sites (7261/7276, 9475) call the deep functions; delete the per-site prefix derivation.
4. Delete getInstallExports / loadInstallExports / InstallExports + the GSD_TEST_MODE bin/install.js require from runtime-artifact-layout.cts.
5. Tests: fast-check property test for the rewrite engine ($HOME-collapse invariant; path-rewrite idempotency), direct _computePathPrefix unit tests, delete the path-replacement.test.cjs reimplementation, and a DEFECT.GENERATIVE-FIX parity guard ensuring no second converter copy reappears.

These phases should NOT

• Bundle ADR-3660 Phase 2 (install/uninstall layout.kinds loop collapse, ~250 lines, separate issue #3664).
• Relocate getConfigDirFromHome or other general install helpers the rewrite engine does not need.

Migration Inventory

New files

• docs/adr/1508-runtime-artifact-conversion-module.md (this ADR) + README index row.
• CONTEXT.md glossary: flip Runtime Artifact Conversion Module [Planned] → shipped, and update the Runtime Artifact Layout Module entry (the getInstallExports seam sentence is removed). (lands with Phase 2)

Phase 1 modified

• src/runtime-name-policy.cts — +getDirName.
• src/runtime-artifact-conversion.cts — +processAttribution, +getCommitAttribution.
• bin/install.js — re-point 13 (getDirName) + 21 (attribution) call sites; delete local convertClaudeToAugmentMarkdown.
• tests — augment characterization test.

Phase 2 modified

• src/runtime-artifact-conversion.cts — +_applyRuntimeRewrites, +both walkers, +computePathPrefix (private) + deep seam.
• src/surface.cts — deep-call cutover; drop the getInstallExports import + prefix math.
• src/runtime-artifact-layout.cts — delete getInstallExports/loadInstallExports/InstallExports + the install.js require.
• bin/install.js — three sites call the deep functions; import them back from the conversion module.
• tests — engine property test, _computePathPrefix unit tests, delete path-replacement.test.cjs reimplementation, parity guard.

Consequences

• + surface.cts and install.js stop re-deriving the path prefix — one owner, leak dissolved at both sites.
• + The .cts source tree no longer reaches into hand-authored bin/install.js; runtime-artifact-layout.cts no longer requires install.js or toggles GSD_TEST_MODE.
• + computePathPrefix gains real unit + property coverage it lacks today.
• − bin/install.js stays hand-authored JS; it now imports the rewrite engine back from the generated conversion.cjs — the same pattern it already uses for hooksSurface and ...runtimeArtifactConversion. Only the moved functions become TypeScript; install.js itself is not converted.
• − Two-phase sequence; CONTEXT.md glossary, ADR README index, and lint:ci (ADR-HEADER) updates required at merge.

Relationship to other ADRs and issues

• ADR-3660 (Runtime Artifact Layout Module): resolves its §Initial Scope deferral ("A future ADR may consolidate them … if a second consumer emerges"). Layout owns placement; this module owns content. Independent of ADR-3660 Phase 2 (#3664).
• ADR-457 (generated-CJS single source): the moved engine is authored in src/*.cts and consumed as generated bin/lib/*.cjs, consistent with the single-source rule.
• ADR-1235 (descriptor-driven agent conversion): complementary — both narrow bin/install.js's ownership of conversion concerns.
• Epic #1507 tracks the phases. Distinct from epic #1258 (cross-runtime skill mapping + plugin skill provision/consumption): #1258 Phase A documents the converter transform-contract catalog; this ADR decides module ownership + dependency direction + engine relocation. Continues #1099 (closed first slice that created the module) and is a sibling of #1173 (agent-converter wiring).