Chore / Docs / CLAUDE.md Phase -1 closure update

[guysenpai]

Summary

Documentation maintenance: bring CLAUDE.md to a Phase −1 closed state now that v0.0.7-S6-ipc-round-trip is tagged on main. No code changes.

8 modifications applied (and only those):

1. Header status block rewritten (~12 lines): tag date 2026-05-18, 7/7 spikes validated, per-spike margins (S1 18×, S3 263×, S4 27×, S5 cold 27× / incremental 1.9×, S6 166×), 3 Phase 0.6 debts, pointer to engine-spec.md §25.3 and engine-phase-0-plan.md.
2. Current state table: Phase 0 (Fondations), milestone none, last tag v0.0.7-S6-ipc-round-trip, branch main, next M0.0 — custom Zig linter + housekeeping.
3. S6 tag row date flipped (planned) → 2026-05-18 and wording cleaned.
4. S6 hypothesis row reworded around the 166× RTT margin.
5. Open / deferred decisions: Custom Zig linter removed (it becomes M0.0); spec/ directory entry reworded for the post-S0 state.
6. Non-negotiable rules: tree-sitter dropped from the C keepers list (Phase −1 decision — the Etch parser is now native Zig in-tree); 8 → 7 everywhere it appeared.
7. Quick links spec: hallucinated filenames fixed — weld-tier0-interfaces.md → engine-tier-interfaces.md, weld-c-api.md → engine-c-api.md. engine-phase-0-plan.md not added to Quick links (KB-only, not in repo).
8. Footer Last updated: already on 2026-05-18 (today) — no change required.

Supersedes #10 (older partial sync attempt).

Test plan

• zig build green locally (pre-push hook ran build + test + test-release, all green)
• git diff main..HEAD touches only CLAUDE.md
• grep -E 'tree-sitter|weld-tier0|weld-c-api|\b8 (authorized|C keepers)' CLAUDE.md returns no matches

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