fix: harden the LOD manifest-builder lane

[eordano]

What

Two independent failure modes in the JIT LOD lane's scene-lod-entities-manifest-builder step, both found by driving a deployment end-to-end:

1. Read-only workdir poisoning. copy_tree seeds the builder workdir with fs::copy, which preserves source permissions. When the tool dir lives in a read-only store (e.g. a Nix package, mode 444), the copied files land read-only; if a first run is interrupted, every later rebuild fails at copy package.json: Permission denied — permanently, since the copy can never overwrite its own read-only output. Every LOD request then 404s lod-build-failed.

2. Inherited CATALYST_URL. The npm child inherits the whole service environment, and the tool resolves its content server from CATALYST_URL — a generic name that deployments commonly set for other services on the same host. When the inherited value points at something that isn't a catalyst content API, the scene run completes with zero entities and the lane emits tiny empty-scene LOD bundles, cached as success — worse than the failure case.

Fix

• copy_tree clears the read-only bit on the destination before and after each copy, so a poisoned tree self-heals and store-sourced trees stay writable.
• The pipeline passes its own catalyst to the npm child as --catalyst=<base> (npm exposes it as npm_config_catalyst, which the tool already prefers over CATALYST_URL), deriving the base by stripping a trailing /content from the pipeline's content URL. Inherited environment can no longer redirect scene fetches.

acquire_placements / run_manifest_builder gain a catalyst parameter; all callers updated.

Verification

• 97 lodgen unit tests pass, plus a new catalyst_base case.
• End-to-end: with a deliberately poisoned workdir (444 package.json) and CATALYST_URL pointing at a dead port, abgen-lod generate on a production scene builds real placements and passes the 32-check self-gate; before the fix the same setup failed instantly (case 1) or emitted empty-scene bundles (case 2).

🤖 Generated with Claude Code