Preserve wrapped Composer overlay package layouts

[chubes4]

Summary

Preserve a Composer dependency overlay as one coherent package when the consumer adds a common wrapper directory to its PSR-4 paths. This keeps package bootstraps, package-local Composer metadata, and source files aligned instead of relocating only source directories.

What changed

• Detect when every comparable PSR-4 mapping adds the same safe wrapper prefix.
• Stage the complete hydrated package under that wrapper and retain the actual package root for source-reference metadata.
• Preserve the existing source-directory relocation behavior for non-wrapper layout changes.
• Strengthen the overlay smoke test to execute a package bootstrap through its relocated classmap and verify no bootstrap or autoloader remains at the old root.

Compatibility

Overlay target paths, checkout immutability, cleanup ownership, source references, and non-wrapper relocation behavior remain unchanged. Wrapper detection fails closed when mappings disagree or any comparable mapping remains unwrapped.

Verification

• npm run test:composer-package-overlay-autoload-layout
• npm run build
• git diff --check

Evidence

Lab run 10b9a5f5-4782-4f77-9b29-cf2afe61d1ac executed WP Codebox #2054 commit 789b5aa5806f914afd4f0c1684af690f4947f930. The repaired WP-CLI response retained 1,047,387 characters, proving the lazy-response fix, but the overlay emitted 138 missing-source classmap warnings and the payload ended mid-JSON. Raw output SHA-256: 1dc2de341beb689dcbc6b37373ed2dcafecd25b3d28534f9567362e7b27409be.

Closes #2055

AI assistance

• AI assistance: Yes
• Tool: Homeboy and OpenCode
• Model: openai/gpt-5.6-sol
• Used for: Traced the Lab-only warning and truncation chain, drafted the generic wrapper-layout repair and executable regression, reviewed the generated edge cases, and ran deterministic verification.

[chubes4]

Lab integration evidence is available from run 50eadcfc-23c9-450a-929f-cb47f08f2a65, using combined WP Codebox commit 427cd1514bd157cc4fcf07cf6744acb1eb7d7d98 (#2054 + this PR).

The package-layout repair removes the previous 138 autoload warnings and allows the structured WP-CLI payload to parse. The fixture now retains the import report, blocks-engine/wordpress-site-plan/v2, a completed materialization receipt, and all eight bounded page provenance records.

The matrix remains red for fixture quality findings, as expected. Evidence readiness improved from five missing fields to one: transformer_reference. That remaining clean-source reference propagation gap is independently tracked in #2058 rather than attributed to this layout repair.