✅ Phase 6: Translation tooling (built & verified; full run deferred to launch)

The build-time AI translation script (D007 - Build-time AI Translation). Tooling done + mock-verified; the real run happens at launch on final English (D015) once the AI key is active. Deployed preview = byte-equivalent English behavior (all mock artifacts removed, manifest reset).

scripts/translate.mjs, npm run translate -- <flags> (the -- matters; bare --dry-run gets eaten by npm). English = sole source. Targets hi, kn, te, ur, ar, hi-Latn. Hinglish has a dedicated prompt, natural casual romanized Hindi ("maine ye app scratch se banaya" register), explicitly NOT transliteration. AI SDK via the same Gateway as /api/ask, Sonnet-class model, temp 0.2, hard-rules system prompt: preserve structure / frontmatter keys / wikilink targets / code / URLs; never translate the 10 product names + tech terms + "Mohd Saif"; RTL for ur/ar; confident-plain-senior tone.

Covers: UI catalogs (only keys MISSING from hand-authored files, Phase 0's 7 per-locale translations provably excluded: plan shows hi needs 131 keys vs hi-Latn 138), all case-study MDX → src/content/work/<locale>/, and --brain (opt-in) for note bodies (36 notes × 6, plan grew automatically as the vault grew).

Safety rails, each verified:

• Dry-run: full plan (6 catalog batches / 799 keys + 24 case studies), zero API calls, zero writes.
• No key → clean exit 0 with "activates at launch (D017)" message.
• Incremental manifest (per-key hashes for catalogs, per-file for MDX/notes): re-run skipped unchanged; a simulated English change re-planned exactly that one file.
• Post-translation validation REJECTS output where URLs / wikilink targets / code fences / frontmatter keys / proper nouns don't survive, failed files reported, never written.
• --mock exercises the full pipeline with no API spend (how it was tested pre-card).

D006 review gate, wired + build-verified both ways: output lands as translationStatus: machine (site keeps English fallback); flipping to reviewed (manifest for catalogs/notes, frontmatter for MDX) makes it live. Proven with a marker: reviewed → shows on /hi/ only; machine → English fallback everywhere, machine MDX never renders.

Latent bug fixed: deepMerge was spreading arrays into objects ({0:…,1:…}), would have corrupted any catalog with arrays.

Launch run: (1) vercel env pull / export key once Gateway card is in; (2) npm run translate -- --sample --only=hi → eyeball → full npm run translate (+--brain to localize the vault); (3) review, flip to reviewed, commit, deploy.

🏁 All six build phases complete. Launch = the 4 env/account actions + metrics + review (see LAUNCH-CHECKLIST.md).