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 MSD_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. Exception: opencode and kilo path-prefix rewriting remains a deliberate bin/install.js-owned pre-conversion step (see applyOpencodeFamilyPathPrefix); this is intentional per #784 and is not a violation of the single-owner rule.
• 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 MSD_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 MSD_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 MSD_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).

Amendment — 2026-06-24: Implementation complete (epic #1507 closed)

The decision recorded above is implemented on next. The ADR Status stays Accepted — per this directory's append-only convention there is no "Implemented" status; this dated amendment records that the decision is realized.

Landed:

• Phase 1 (#1512): getDirName → src/runtime-name-policy.cts; processAttribution → src/runtime-artifact-conversion.cts. (getCommitAttribution stays in bin/install.js — a documented scope refinement: it is impure install-time config I/O, not a content-transformation helper, so it cannot move into the pure conversion module. Phase 2 injects the resolved attribution value instead.)
• Phase 2 (#1513): the content-rewrite engine (_applyRuntimeRewrites), both staged-content walkers, and computePathPrefix (private; _computePathPrefix for tests) live in src/runtime-artifact-conversion.cts behind the deep seam rewriteStagedSkillBodies / rewriteStagedCommandBodies({runtime, configDir, scope, homedir?, platform?, resolveAttribution?}). The getInstallExports / loadInstallExports / InstallExports relay and the MSD_TEST_MODE install.js require are deleted from src/runtime-artifact-layout.cts — the last upward .cts → bin/install.js dependency is gone. CONTEXT.md marks the module SHIPPED. (The install-side cutover lands one indirection deeper than the literal issue text — install.js delegates to createRuntimeArtifactInstallPlan, which performs the deep calls in src/runtime-artifact-install-plan.cts — satisfying the same dependency-direction intent with a cleaner owner.)

Two deferred follow-ups were spun out as sub-issues of #1507 and have since been delivered (neither was a blocker; the architectural goal — single ownership, downward dependency direction, relay deletion — was already met by the merged slices above):

• #1675 (PR #1685) — deduped the byte-identical convertClaudeToAugmentMarkdown / convertSlashCommandsToAugmentSkillMentions between bin/install.js and the conversion module (the Phase 1 → Phase 2 deferred cleanup; install.js now binds them from the conversion module, single-sourced).
• #1676 (PR #1686) — added the fast-check property test ($HOME-collapse invariant + path-rewrite idempotency) promised in #1511's test scope.

Delivery verified by a Codex (gpt-5.4, high-effort, read-only) review against the epic's stated deliverables, cross-checked against the indexed code graph and live source.

Amendment — 2026-08-17 (#2876): the re-export mandate's stated beneficiary was the test suite

This ADR's relocation slices, and ADR-857's before them, kept a re-export spine in bin/install.js so that "existing consumers that do require('../bin/install.js').writeCursorHooksJson (etc.) continue to work unchanged" — the wording carried in src/runtime-hooks-surface.cts's own header.

Epic #2866 Phase 7 measured the consumers. There are none.

bin/install.js exported 197 names. Every reference to it outside tests/ — in src/, hooks/, scripts/ and bin/ — sits inside a comment, including the one in runtime-hooks-surface.cts that named the case. Not one line of production code has ever required the file. The 44 consumers are test files.

So the pattern was real and the reasoning behind it was sound; the beneficiary was simply misidentified. The compatibility spine was preserving access for a caller that did not exist, while the actual dependency — the test suite reaching implementation through the installer rather than through the modules that own it — went unnamed and therefore unmanaged.

What Phase 7 changed. 9 dead exports and 61 pass-throughs are gone; their tests now import the extracted modules directly. bin/install.js exports 127 — 197 − 9 − 61 — and every one of those 127 is substantive local implementation. They are not a compatibility wall; they are code with no other home yet, and extracting them is a different piece of work.

What this does not change. The dependency direction this ADR established — installer and layout import the conversion module, the conversion module imports nothing upward — is untouched, and so is ADR-857's capability-registry contract. Relocation still requires the moved symbol to keep working for its real callers; the correction is only about who those callers are.

The generalizable point. A back-compat re-export is a claim about consumers, and a claim about consumers is checkable. This one went four ADRs and several epics without being checked, which let an interface be shaped by test access while everyone believed it was shaped by callers. Before adding a compatibility layer, enumerate what it is compatible for; if the answer is "the tests", the honest fix is to point the tests at the owning module.