Bun Standalone Graph and JSC Cache Deep Dive

This page narrows one question: what can be recovered from the Bun container in the signed Claude Code 2.1.177 Mach-O, and what would be false precision? It uses the committed provenance, binary inventory, derived topology, and the version-pinned Bun StandaloneModuleGraph.zig. It publishes no recovered module content, JSC cache bytes, or native payloads.

Evidence basis

Observed The artifact is a thin arm64 Mach-O of 225,124,512 bytes with SHA-256 eb073035…e40ed9. Its embedded runtime string is 1.3.14+2a41ca974. The nine-character revision prefix resolves to pinned Bun commit 2a41ca974b7302952252a20eddbb3b5c3f2dee9b; the full revision is a derived lookup recorded in provenance, not a string carried in the Claude binary.

Observed in pinned Bun source A serialized module record contains six offset/length pointers—for name, content, source map, bytecode, module information, and bytecode origin—followed by one byte each for encoding, loader, module format, and side. That yields the 52-byte record size used by the public parser.

Byte layout

Observed Mach-O load commands name one __BUN,__bun section. Its first eight bytes hold the payload length. The payload ends with a 32-byte offsets record and the 16-byte Bun trailer; the offsets record says the preceding graph is 150,764,682 bytes.

flowchart LR
    accTitle: Bun Standalone Graph and JSC Cache Deep Dive - Byte layout
    accDescr: Diagram showing byte layout in the Bun Standalone Graph and JSC Cache Deep Dive section.
  A["File 0..72,368,128<br/>Mach-O bytes before __bun"]
  B["8-byte payload length<br/>72,368,128..72,368,136"]
  C["Graph bytes<br/>150,764,682 bytes"]
  D["Offsets record<br/>32 bytes"]
  E["Bun trailer<br/>16 bytes"]
  F["File suffix<br/>1,991,646 bytes"]
  A --> B --> C --> D --> E --> F

  C -. contains .-> G["Entrypoint JSC cache<br/>payload 120..129,119,608"]
  C -. contains .-> H["Entrypoint deployed JS<br/>payload 129,119,680..146,157,776"]
  C -. ends with .-> I["11 × 52-byte module table<br/>payload 150,764,109..150,764,681"]

Derived “Before” and “suffix” in the diagram are coordinate partitions, not claims that those bytes are opaque to every Mach-O tool. The topology generator deliberately classifies only the Bun section; ordinary native segments, load commands, signatures, and link-edit data remain the Mach-O parser’s responsibility.

Layout landmarks

Region	Coordinate system	Start	End, exclusive	Bytes
__BUN,__bun	file	72,368,128	223,132,866	150,764,738
payload	file	72,368,136	223,132,866	150,764,730
graph bytes	payload	0	150,764,682	150,764,682
module table	payload	150,764,109	150,764,681	572
offsets record	payload	150,764,682	150,764,714	32
trailer	payload	150,764,714	150,764,730	16

Observed The graph flags value is 15. Under the pinned Bun Flags layout, all four defined bits are set: disable default environment files and disable autoload of bunfig, tsconfig, and package.json. This is a compile-container setting; it does not mean Claude Code ignores its own settings files.

Module table

Observed The table has 11 records: six Latin-1 CJS/JavaScript records on the serialized server side and five binary N-API records on the serialized client side. “Client” and “server” are Bun enum values here; this evidence does not reinterpret them as a browser/server deployment split.

#	Virtual module	Loader / format / side	Content bytes	JSC cache bytes
0	/$bunfs/root/src/entrypoints/cli.js	js / cjs / server	17,038,096	129,119,488
1	/$bunfs/root/image-processor.js	js / cjs / server	1,976	0
2	/$bunfs/root/audio-capture.js	js / cjs / server	1,974	0
3	/$bunfs/root/url-handler.js	js / cjs / server	1,972	0
4	/$bunfs/root/computer-use-swift.js	js / cjs / server	1,979	0
5	/$bunfs/root/computer-use-input.js	js / cjs / server	1,979	0
6	/$bunfs/root/image-processor.node	napi / none / client	1,249,368	0
7	/$bunfs/root/computer-use-swift.node	napi / none / client	879,672	0
8	/$bunfs/root/computer-use-input.node	napi / none / client	1,692,096	0
9	/$bunfs/root/audio-capture.node	napi / none / client	438,112	0
10	/$bunfs/root/url-handler.node	napi / none / client	336,864	0

Observed Content totals 21,644,088 bytes; bytecode-cache storage totals 129,119,488 bytes. Every source map and module-information pointer has size zero. The inventory hashes each content region independently but intentionally does not publish its bytes.

Deployed source versus JSC cache

Observed Module 0 has two separate pointers in the same record: a 17,038,096-byte deployed JavaScript/CJS content region and a 129,119,488-byte bytecode-cache region. Its bytecode origin path is exactly the module name, /$bunfs/root/src/entrypoints/cli.js.

Observed in pinned Bun source Bun stores the path used to generate bytecode because it must match at runtime for a cache hit. For Mach-O’s eight-byte section header, Bun targets payload offset modulo 128 equal to 120, making the cache’s file address 128-byte aligned. This artifact matches both conditions: payload offset 120 and file offset 72,368,256, whose modulo 128 is zero.

Derived The JSC region is a runtime-specific cache paired with—not a replacement for—the deployed content. Its size must not be interpreted as source complexity: the pinned serializer can include alignment and trailing cache storage, and the format is coupled to runtime expectations and the origin path. This project therefore locates and sizes the cache but does not present it as a portable intermediate language or attempt to turn it back into proprietary source.

Observed The cache ends at payload offset 129,119,608 and the deployed content begins at 129,119,680. The 72-byte gap is recorded as a coordinate fact only; no semantic meaning is assigned to it.

Native boundary map

Derived Five small CJS modules and five N-API records share virtual basenames. Basename pairing is strong evidence of wrapper/add-on boundaries, but it does not establish exports, argument schemas, call frequency, or permission behavior.

Boundary label	JavaScript wrapper	N-API payload	Native bytes
image-processor	module 1	module 6	1,249,368
audio-capture	module 2	module 9	438,112
url-handler	module 3	module 10	336,864
computer-use-swift	module 4	module 7	879,672
computer-use-input	module 5	module 8	1,692,096

flowchart LR
    accTitle: Bun Standalone Graph and JSC Cache Deep Dive - Native boundary map
    accDescr: Diagram showing native boundary map in the Bun Standalone Graph and JSC Cache Deep Dive section.
  JS["Small CJS wrapper"] --> NAPI["Opaque .node / N-API module"]
  NAPI --> OS["OS-native capability surface"]
  APP["Bundled CLI entrypoint"] --> JS

Observed The outer executable uses the hardened runtime and carries entitlements for JIT, unsigned executable memory, disabled library validation, and audio input. Entitlement presence is a security-envelope fact, not proof that a particular module exercised the capability in a given run. The independently authored native boundary reconstruction keeps these interfaces opaque.

Parser invariants

The read-only parser fails closed on structural ambiguity:

1. Implemented Require a thin, little-endian, 64-bit Mach-O and fully bounded load-command table.
2. Implemented Require exactly one __BUN,__bun section with matching segment/section names.
3. Implemented Treat every offset and size as a safe integer and reject any slice outside its owner.
4. Implemented Require the payload to fit the section, the trailer to match, and graph byte count to equal the offsets-record start.
5. Implemented Require module-table size divisible by 52, an in-range entrypoint, and bounded module pointers.
6. Implemented Require NUL terminators for names, contents, bytecode-origin paths, and compile argv.
7. Implemented Keep extraction optional, path-contained, collision-checked, and N-API payloads excluded unless explicitly requested.

Derived These checks establish memory-safe parsing of this declared layout; they do not authenticate semantic meaning. Artifact identity still comes from the binary hash and code signature, while format interpretation comes from the pinned Bun revision.

What is and is not recoverable

Recoverable from this artifact	Not established or not recoverable faithfully
Exact container ranges, module records, virtual names, sizes, encodings, loaders, sides, formats, and content hashes	Original source-repository layout, package boundaries, build configuration, comments, formatting, and most original identifiers
Local deployed JavaScript contents at bounded offsets	A claim that the deployed 17 MB bundle is the original source tree
Presence and coordinates of one JSC cache plus its origin path	Reliable high-level source reconstruction from JSC cache bytes
Five local N-API payload ranges and wrapper-name pairings	Native source code, complete exports, argument contracts, or runtime permission behavior
Short anchored literals and their offsets	Full proprietary prompts, code, or a redistribution right
One embedded Anthropic build Git SHA	Access to, or identity of, a public upstream Anthropic source repository

Observed The bundle preserves at least one source-like path literal—src/tools/BashTool/readOnlyValidation.ts—as recorded by anchor tools.bash-readonly-source. Such survivors are useful anchors, not evidence that the original file tree can be reconstructed.

Deterministic validation

build-binary-topology.mjs reads only the two committed JSON inputs, checks their shared artifact identity and layout invariants, and emits no timestamps. Rebuild and compare it with:

node tools/build-binary-topology.mjs /tmp/binary-topology.json
cmp evidence/binary-topology.json /tmp/binary-topology.json
node --check tools/build-binary-topology.mjs
npm run check

The generated JSON includes SHA-256 digests of both source evidence files, so a later metadata change cannot masquerade as the same derived topology.