chore: remove orphaned old engine (dead code) (issue #42)

devlog/2026-08-05_remove-old-engine/REQ.md

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+# REQ — remove orphaned old engine (dead code)
+
+Issue: dog/opencode-acp#42 (follow-up) · Branch: `2026-08-05_remove-old-engine`
+Base: `2026-08-05_acp-kernel` (stacked; retarget to master after PR #274 merges)
+
+## Problem
+
+After the one-shot acp-kernel rewrite (PR #274), the old in-tree compression
+engine was left on disk as dead code (unreferenced by `index.ts`, tree-shaken
+from `dist/`). @dog directed: **"旧代码可以直接删除 在新分支"** — delete it, on a
+new branch.
+
+## Goal
+
+Remove every source file and test that is no longer reachable from `index.ts`,
+so the source tree matches what actually ships.
+
+## Acceptance criteria
+
+- `npm run typecheck` — PASS (no dangling imports).
+- `npm run build` — PASS; `dist/index.js` byte-identical to pre-deletion (proves
+  the removed code was already dead/tree-shaken — zero runtime impact).
+- `npm test` — PASS, 0 fail. Remaining tests cover only kernel + shared infra.
+- No file reachable from `index.ts` is deleted (verified by transitive
+  import-closure trace).
+
+## Scope
+
+Computed via transitive relative-import closure from `index.ts`
+(`scripts`-style trace, see WORKLOG). DEAD = unreachable.
+
+- **51 dead source files** removed: `lib/hooks.ts`, `lib/compress-permission.ts`,
+  whole `lib/commands/`, `lib/gc/`, `lib/ui/`, `lib/compress/quality-gate/`,
+  `lib/messages/filter/`, `lib/messages/inject/`, plus selected files in
+  `lib/compress/`, `lib/messages/`, `lib/prompts/`.
+- **47 dead test files** removed (those importing any dead module).
+- **KEPT** (still reachable): all of `lib/kernel/`, shared infra
+  (`config`, `logger`, `token-utils`, `auth`, `update`, `host-permissions`,
+  `config-validation`), and selected old modules the kernel adapter / infra
+  still import (`lib/messages/{query,shape}.ts`, `lib/prompts/*` except the
+  dead extensions, `lib/state/*`, `lib/message-ids.ts`, `lib/protected-patterns.ts`,
+  parts of `lib/compress/`).

devlog/2026-08-05_remove-old-engine/WORKLOG.md

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+# WORKLOG — remove orphaned old engine (dead code)
+
+Issue: dog/opencode-acp#42 (follow-up) · Branch: `2026-08-05_remove-old-engine`
+Base: `2026-08-05_acp-kernel`
+
+## Method
+
+Computed the exact dead set via a transitive relative-import closure trace from
+`index.ts` (script at `/tmp/opencode/trace-deps.mjs`):
+
+1. BFS from `index.ts` over relative imports → **KEEP set** (41 files).
+2. `lib/` files not in KEEP → **DEAD source** (51 files).
+3. Tests whose imports resolve into any DEAD source file → **DEAD tests**
+   (47 files); remaining 28 test files kept.
+
+This guarantees no reachable file is deleted — only genuinely orphaned code.
+
+## Removed (51 source files)
+
+- Whole dirs: `lib/commands/`, `lib/gc/`, `lib/ui/`, `lib/compress/quality-gate/`,
+  `lib/messages/filter/`, `lib/messages/inject/`.
+- `lib/hooks.ts`, `lib/compress-permission.ts`.
+- `lib/compress/`: decompress-logic, decompress, hide-consumed, hide-failed,
+  index, keep-markers, parts, pipeline, range, recap, status.
+- `lib/messages/`: index, priority, prune, reasoning-strip, sync,
+  truncate-tools, utils.
+- `lib/prompts/`: extensions/nudge, extensions/tool, index.
+
+## Removed (47 test files)
+
+All tests that imported a dead module (e.g. `tests/compress-range.test.ts`,
+`tests/inject.test.ts`, `tests/e2e-*.test.ts`, `tests/quality-gate-*.test.ts`,
+`tests/gc-merge.test.ts`, `tests/hooks-permission.test.ts`, …). Full list in
+the trace output.
+
+## Kept (reachable old modules — NOT dead)
+
+The kernel adapter / shared infra still import these, so they must stay:
+`lib/messages/{query,shape}.ts`, `lib/prompts/{system,store,compress-range,
+context-limit-nudge,iteration-nudge,turn-nudge,extensions/system}.ts`,
+`lib/state/{index,persistence,rebuild,state,tool-cache,types,utils}.ts`,
+`lib/compress/{protected-content,range-utils,search,state,timing,types}.ts`,
+`lib/message-ids.ts`, `lib/protected-patterns.ts`, `lib/config-validation.ts`.
+
+## Verification
+
+- `npm run typecheck` — **PASS** (0 errors; no dangling imports).
+- `npm run build` — **PASS**. `dist/index.js` = **175.53 KB**, byte-identical
+  to pre-deletion → the removed code was already tree-shaken; **zero runtime
+  impact**, pure source-tree cleanup.
+- `npm test` — **PASS** (336 tests, 0 fail). Test count dropped 961 → 336
+  (−625), exactly the dead-engine tests.
+- `scripts/ci/check-pr.sh 2026-08-05_remove-old-engine github/master` — PASS
+  (branch name, devlog REQ+WORKLOG present, version unchanged).
+
+## Notes
+
+- The identical `dist/` size confirms the earlier claim in PR #274's WORKLOG:
+  the old engine was already fully tree-shaken from the published bundle. This
+  PR is a source-hygiene follow-up, not a behaviour change.
+- PR is stacked on `2026-08-05_acp-kernel` (base). Retarget to `master` once
+  PR #274 merges. Alternatively @dog may fold both into one merge.