Imported from huybuidac/claude-code-patchkit (skills/claude-patch/SKILL.md). Install upstream with npx skills add huybuidac/claude-code-patchkit --skill claude-patch. Copyright stays with the author.

claude-patch

Binary patches for Claude Code CLI — unlock hard-coded limitations without waiting for upstream changes.

All scanning and patching runs through one cross-platform tool, patches/patch-bin.js. It handles ad-hoc re-signing on macOS and the rename-swap a locked claude.exe needs on Windows, so there are no per-platform scripts to choose between.

node patches/patch-bin.js scan   --patch <name> [--bin <path>]   # state + derived anchor + guards
node patches/patch-bin.js apply  --patch <name> [--bin <path>]
node patches/patch-bin.js revert --patch <name> [--bin <path>]
node patches/patch-bin.js status [--bin <path>]                  # scan every patch
node patches/patch-bin.js list                                   # registered patch ids

--bin defaults to the resolved claude on PATH. scan exits 1 when the state is abnormal or patched-inert, status when any patch is.

Workflow

1. Identify the binary — run scan; it prints the resolved path, size, and state. Show the user the path and claude --version before proposing any write.
2. Select the patch — from the user's argument, or ask. Read patches/<name>.md for what it does and what it is tested on.
3. Confirm — never write without explicit user confirmation for this specific binary.
4. Apply or revert — apply handles guard checks, backup, the write, the sidecar, re-signing, and self-verification in one step, and refuses rather than guessing if anything is off.
5. Report — state the resulting marker count, and that a restart is needed. (Earlier docs claimed subagent-model took effect without one; that was never demonstrated and the one time it was checked, the session had been restarted.)

Never report a patch as working from a marker count alone. Since 2.1.250 a marker can sit in a binary that ignores it — see Bytecode shadowing. scan now catches this, but the durable check is behavioural: claude mcp serve speaks JSON-RPC on stdio, so an initialize + tools/list round-trip prints the live tool schemas without spending a token.

Available patches

Commands: apply <patch>, revert <patch>, status (scan every patch), list.

Safety rules

• NEVER patch without explicit user confirmation.
• NEVER patch if a context guard fails — apply enforces this, so do not work around it.
• If state is abnormal, abort and report. Both-zero (no anchor, no marker) means the fingerprint changed: re-derive it before doing anything else, never patch blind.
• A marker is not proof the patch works. patched means marker present and nothing shadowing it; patched-inert means the write landed on code that never runs.
• Every write is length-preserving and verified against the expected bytes at that offset first, so a stale offset aborts instead of corrupting the binary.
• Backups (<binary>.bak.<ts>) are ~290 MB each. Mention rotation after a version is confirmed working.

Why anchors are derived, not hardcoded

Every literal anchor in this skill's history eventually matched 0 times, because the bundler renames minified identifiers every few builds. A count of 0 is indistinguishable from "the feature was removed", so a hardcoded anchor turns routine drift into a false abort.

Each patch therefore derives its anchor at scan time from landmarks that do not move — string literals the product ships (.describe() text, source:"…" labels) and positional locals the bundler assigns by position. Patch definitions document the derivation rule rather than the bytes. When adding a patch, find a landmark first; if the only stable thing you can find is a minified name, expect it to rot.

Bundle multiplicity

The bun-compiled binary may embed the JS bundle more than once:

• macOS ≤ 2.1.132: 2 instances; macOS ≥ 2.1.133: 1
• Windows: 1 (all observed versions)

Never hard-assert a count — derivation counts landmarks and patches all of them.

Bytecode shadowing

At 2.1.250 the binary began shipping a JSC bytecode copy of each module alongside the JS source and running the bytecode. The source is still complete and still what every patch here edits — it just stops being what executes. A source-only patch then leaves the marker in the file and changes nothing, which the old scan reported as a clean patched.

The fix is not to patch bytecode. bun's embedded module graph gives each module a bytecode slice, and an empty slice means "not cached, compile the source". So apply zeroes the 4-byte length of that slice for the module holding the patch site, and the source patch becomes live.

trailer magic "\n---- Bun! ----\n"
  byte_count u64 @ magic-32   →  base = (magic-32) - byte_count
  modules_ptr (u32 off, u32 len) @ magic-24
record = 52 bytes: name, contents, sourcemap, bytecode, module_info,
         bytecode_origin_path  (6× StringPointer{u32 offset, u32 len})
         + encoding, loader, module_format, side (4× u8)

The record is found by asking which module's contents range contains the patch offset — never by chunk name, which is content-hashed and changes every build. Layout is from bun's src/standalone_graph/StandaloneModuleGraph.rs; if the trailer does not decode, scan says so and apply warns rather than guessing.

Cost is one module compiled at startup instead of loaded: ~50 ms measured on 2.1.250 for the 3.9 MB chunk holding the Agent tool (init 0.235s → 0.283s). Other modules keep their bytecode.

Two states matter:

• patched-inert — marker present, bytecode still shadows it. Re-run apply; it repairs in place (bytecode edit only, source untouched) rather than refusing.
• Binaries ≤ 2.1.239 run from source and need no bytecode edit. Their graph may not decode with the layout above, which is reported, not fatal.

Verified end to end on 2.1.250 macOS arm64: pristine → apply → Agent tool model loses its enum and a subagent really runs on gpt-5.6-luna[1M]; revert → enum returns.

Revert

revert prefers the sidecar <binary>.rtk-<patch>.json that apply writes: it records the original bytes for each offset, so the reverse-patch is exact and immune to build mismatch. This matters because a patched binary alone cannot reconstruct a drifted alias — only its length survives. Its graphEdits array holds the original bytecode-slice lengths, restored the same way; a sidecar written before that field existed reverts the source sites and leaves the graph alone.

Without a sidecar (patched before they existed) it falls back to a content-validated backup: the candidate must itself scan as unpatched with matching landmarks and guards. Do not gate on file size — on macOS the backup is Apple-signed while the patched binary is ad-hoc signed, so their sizes legitimately differ. A <binary>.preRevert.<ts> snapshot is taken before any write, so the revert itself is undoable.

Platform notes

• macOS — patching invalidates Anthropic's signature; apply/revert re-sign ad-hoc and verify. Gatekeeper may prompt on first launch.
• Windows — a running claude.exe is locked, so writes go to a copy that then takes the original's path (renaming a running image only updates the directory entry). Authenticode becomes HashMismatch; the binary still runs, though SmartScreen/AppLocker policy may object. A displaced *.replacing.* file may linger until the old process exits.
• Auto-update — each new Claude Code version ships a fresh, unpatched binary. Re-apply per version.

Contributing

To add a new patch, create ${CLAUDE_SKILL_DIR}/patches/<name>.md following patches/TEMPLATE.md, and register its derivation in patch-bin.js.