feat: in-process Lua core handler for claudecode (#47, phase 3)

[Cannon07]

Summary

Phase 3 of #47 — ports the bash core handler to in-process Lua and flips the Claude Code backend to use it. Backends still on bash (opencode/codex/copilot/gemini) continue working unchanged; they flip in follow-up PRs.

Architectural choice (see ADR-0005): the new handler runs in-process inside the user's Neovim via a single RPC call, not as a headless worker. This eliminates the per-proposal cold-start (~50–100ms × every Edit / Write / MultiEdit / ApplyPatch) and collapses 5+ RPC round-trips per proposal into one. Issue #47 originally framed phase 3 as a like-for-like swap to a headless worker; the ADR records why we deviated.

What changed

• New: lua/code-preview/pre_tool/{init,bash_detect,normalisers,emitters}.lua — orchestration, Tier 1 Bash detection, per-backend dispatch tables.
• New: lua/code-preview/post_tool.lua — post-tool cleanup.
• New: lua/code-preview/apply/{edit,multi_edit,patch}.lua — extracted from bin/apply-*.lua as pure Lua modules; bin/apply-*.lua now thin shims for external callers.
• Rewritten: backends/claudecode/code-{preview,close}-diff.sh — one nvim_call into the new in-process handler, abstain (exit 0) when nvim is unreachable.
• Tests: 41 new specs across tests/plugin/pre_tool_{bash_detect,normaliser,handle}_spec.lua, including regressions for the it\'s-mine.txt apostrophe-escape case (a fix that goes beyond pure bash parity).
• Docs: ADR-0005 (new), glossary updates to Core handler, Headless worker, Hook context query, ADR-0004 xref.

Behavioural contract

• Claude Code now goes through in-process Lua.
• opencode/codex/copilot still go through bin/core-{pre,post}-tool.sh.
• Both paths land in the same changes / neo_tree / diff modules and serialise on the main loop — no concurrency hazard during the per-backend rollout.
• When the user's Neovim is unreachable, the shim abstains (exit 0, no stdout): Claude Code falls back to its native permission flow, exactly as if the plugin weren't installed.

Out of scope

• Windows .cmd / .ps1 shims — tracked in Request Windows 11 support #46, will consume the in-process Lua landed here.
• Deletion of bin/core-{pre,post}-tool.sh and jq/lsof healthcheck cleanup — happens in a separate cleanup PR after the last backend flips.
• diff.lua refactor — separate.

Test plan

• All existing plugin specs still pass (./tests/run_lua.sh): 63 success / 0 fail / 0 error
• Edit / Write / MultiEdit proposals open a diff and prompt for permission
• Bash with rm <file> marks the file deleted in neo-tree (no diff tab)
• Bash with rm it\'s-mine.txt correctly highlights (new beyond bash parity)
• Bash with echo x > newfile.txt marks bash_created
• Post-tool closes the diff and clears the change indicator
• diff.defer_claude_permissions = true suppresses the ask prompt
• diff.visible_only = true skips diffs for non-visible files

🤖 Generated with Claude Code