orca/docs/reference/xterm-patch-regeneration.md

xterm Patch Regeneration

Scope

Orca ships @xterm/xterm with four source changes it needs and upstream has not taken: the IME composition hooks, the xterm-composition-* custom events they raise, the ICompositionHelper surface those hooks widen, and a SortedList fix. pnpm applies them through config/patches/@xterm__xterm@<version>.patch.

That patch touches eight files. Four are hand-authored source (src/browser/CoreBrowserTerminal.ts, src/browser/Types.ts, src/browser/input/CompositionHelper.ts, src/common/SortedList.ts) and four are the build output those sources produce (lib/xterm.js, lib/xterm.mjs, and both sourcemaps). The bundle half is 7.3 MB of minified code. It is generated, and this document exists so nobody edits it by hand.

The two halves are the same edits diffed two ways, so the generator requires them to match byte for byte on every source file. A hunk the shipped patch cannot name — upstream's .npmignore strips src/**/*.test.ts — would be dropped by the next --write, so it fails the run instead.

config/patches/xterm-src/@xterm__xterm@<version>.src.patch is the source of truth. Everything else is derived from it by config/scripts/regenerate-xterm-patches.mjs, which is pinned to the exact upstream commit the published tarball was built from.

@xterm/addon-webgl, @xterm/addon-search, @xterm/addon-serialize and @xterm/addon-image are generated the same way, from their own source patches under config/patches/xterm-src/. Their entries differ only in packageDir and build steps; everything below applies to all five. @xterm/addon-ligatures is the one patch still written by hand — see Known Gaps.

The image patch bounds pending Kitty decoders by their maximum WASM capacity and caps transmitted image blobs by byte size. Both use the configured storage budget; upstream's displayed-pixel budget does not cover these allocations. Byte-budget eviction drops unplaced payloads first, so a new upload cannot erase a visible image while abandoned blobs still hold budget; displayed images go only when that is not enough, because the cap is a hard bound. The incoming image is always stored, so the cap overshoots by at most one payload rather than dropping an image the protocol already acked as OK. Orca uses fixed 32 MB storage and 8 MiB sequence limits, not arbitrary addon configurations. config/scripts/xterm-image-memory-contract.test.mjs exercises the installed bundle with unfinished uploads, chunk continuation, both eviction orders and disposal. The patch also bounds decompression before joining decoded chunks, validates PNG dimensions before native decoding, and closes stale asynchronous image results after reset, disable or disposal. config/scripts/xterm-image-lifecycle-contract.test.mjs exercises those boundaries against the installed addon. Font zoom scales visible tiles without creating enlarged full-image canvases; config/scripts/xterm-image-resize-contract.test.mjs checks allocation and tile mapping.

Rules

1. Never edit config/patches/@xterm__*@<version>.patch. Edit the source patch and regenerate.
2. Never edit lib/ inside a patched node_modules tree and re-run pnpm patch-commit. That is how bundle hunks stop matching their sources.
3. Every source change must land together with the regenerated bundle hunks and the pnpm-lock.yaml hash bump, in one commit.
4. The upstream commit lives in config/patches/xterm-upstream.json, not in a comment. A version bump that leaves it stale fails the generator, it does not silently patch the wrong tree.
5. Sourcemaps move with the bundle, and are never silently omitted. The patch moves the code, so dropping only the map hunks would ship offsets pointing at the wrong lines. sourcemaps.policy accepts include and nothing else: it costs about 5.8 MB of the emitted patch and is required because src/renderer/src/components/terminal-pane/terminal-ime-xterm-transaction-events.test.ts reads lib/*.map and asserts the mapped Version.ts matches the runtime version. Deleting the maps was once an option; the code that did it was removed as unreachable, so re-adding the policy means re-adding that code.
6. --check is the authority on the lockfile, not pnpm install. pnpm writes the patch hash in two places — patchedDependencies and every resolution key that depends on the patched package — and on a warm store it will leave the resolution keys at their previous value while reporting success. That installs locally and drifts on CI's cold store. For a version bump, follow the Version Bumps workflow through step 5 (the final --check); if it reports a stale hash after an install, rerun --write. For a source-only edit, the four-step workflow above ends at --check.

Workflow

# 1. Edit the source hunks.
$EDITOR config/patches/xterm-src/@xterm__xterm@6.1.0-beta.303.src.patch

# 2. Rebuild the bundle hunks, the full patch, and the lockfile hash.
node config/scripts/regenerate-xterm-patches.mjs --write

# 3. Reinstall so node_modules picks up the new patch hash.
pnpm install

# 4. Confirm the tree is self-consistent.
node config/scripts/regenerate-xterm-patches.mjs --check

Editing a patch file by hand is awkward for anything larger than a one-liner. For a substantial change, work in the generator's own checkout instead — after any run it is left at the pinned commit with the source patch applied:

node config/scripts/regenerate-xterm-patches.mjs --check --work-dir=/tmp/xterm
$EDITOR /tmp/xterm/upstream/src/browser/input/CompositionHelper.ts
git -C /tmp/xterm/upstream diff -- src/ > config/patches/xterm-src/@xterm__xterm@6.1.0-beta.303.src.patch
node config/scripts/regenerate-xterm-patches.mjs --write --work-dir=/tmp/xterm

For an addon, edit under addons/<name>/ and take the diff from that directory with --relative, so the patch is rooted at the package the way the published tarball is:

$EDITOR /tmp/xterm/upstream/addons/addon-webgl/src/TextureAtlas.ts
git -C /tmp/xterm/upstream/addons/addon-webgl diff --relative -- src/ \
  > config/patches/xterm-src/@xterm__addon-webgl@0.20.0-beta.299.src.patch

--write rewrites the source patch into the canonical form it would emit on a re-diff, so a hand-produced git diff gets normalized on the first run rather than fighting --check forever.

Run the checkout outside this repository. A build tree underneath it makes tsgo walk up into Orca's own node_modules and fail with TS2300: Duplicate identifier, which is a symptom of where the tree sits and not of the patch.

How the Commit Is Known

Upstream bin/publish.js sets packageJson.commit before npm publish, so each published tarball names the commit that built it. The generator asserts that stamp against xterm-upstream.json and then compares the tarball's src/ against the checkout file by file. Only src/common/Version.ts may differ, because publish.js rewrites the version immediately before packaging; the generator applies the same stamp.

That pair of checks is what makes the rebuild trustworthy. Without them a wrong commit would still produce a plausible-looking 7 MB patch.

Build Order

Upstream's publish path is npm ci → stamp Version.ts → npm run package. npm run package runs webpack for lib/xterm.js and then, via postpackage, bin/esbuild_all.mjs --prod for lib/xterm.mjs.

An addon needs three steps, in this order, and the first is easy to miss:

1. root npm run build. The addon's own npm run build is tsgo -p . against a tsconfig whose files and include are both empty and which only lists project references. In -p mode tsgo does not build references, so it succeeds while emitting nothing, and the addon's webpack then fails on a missing ./out/. The root build is what populates it.
2. addon npm run package — the addon's own webpack, which emits the CJS lib/addon-*.js. The root package script never builds this.
3. root npm run esbuild-package — bin/esbuild_all.mjs --prod, which emits the ESM lib/addon-*.mjs for every addon at once.

Do not run npm run setup after the packaging build. setup is the development esbuild pass with minify: false. Running it afterwards overwrites lib/xterm.mjs with an unminified bundle and a map that no longer matches, and the resulting patch is silently wrong — the failure mode is a .mjs that is 50% larger than the published one, which is easy to miss inside a 7 MB diff. forbiddenBuildScripts in the manifest encodes this and the generator refuses to run a build step that names one of those scripts.

The generator also builds the unmodified commit first and asserts that it reproduces the published lib/ byte for byte before it emits anything. A toolchain or build-order problem therefore surfaces as an explicit "did not reproduce the published bundles" error rather than as 7 MB of mystery diff.

Recovering From Hand-Edited Bundles

Between 2026-08-09 and 2026-08-17 this harness did not exist, and four fixes landed by editing the minified bundles directly. The tell is code no minifier emits: const in an otherwise let-only bundle, and identifiers like $rl, $hp, $tid.

Recovery is not a rewrite. The hand-edits were applied to src/ as well, so the source hunks in the shipped patch were already correct and --write re-derives the bundles from them. What changes is cosmetic and expected:

• Hand-written locals collapse back into minifier names, which shifts esbuild's frequency-ordered allocation and can swap two short names bundle-wide (i↔t in the .mjs, w↔y in the .js). Most differing lines are the same length.
• Hand-written equivalents normalize to what the toolchain actually emits (!!x back to Boolean(x), an escaped \u200E back to the literal character).

To confirm a regeneration is semantically a no-op rather than a revert, compare identifier multisets between the old and new bundle instead of reading the diff: every name that is not a single-letter minifier local should appear the same number of times in both. Anything else is a real change and needs explaining.

The Lockfile Moves With the Patch

pnpm derives the patchedDependencies hash in pnpm-lock.yaml — and the .pnpm/@xterm+xterm@<version>_patch_hash=<hash>/ store directory name — from the sha256 of the patch file itself. A regenerated patch without the lockfile bump fails pnpm install --frozen-lockfile on every machine except the author's. --write makes that edit; --check fails if it is missing.

config/scripts/regenerate-xterm-patches.test.mjs asserts the same thing without a network or a build, so the ordinary test job catches lockfile drift in milliseconds even though the full rebuild runs in its own CI lane.

Toolchain Pin

toolchain in the manifest records what upstream's package-lock.json resolves at the pinned commit, and the generator fails if npm ci produces something else. The entry that matters is @typescript/native-preview (tsgo), which upstream pins to a dated development build — 7.0.0-dev.20260521.1 at the time of writing. It is a real published version and npm does not prune old releases, but it is the one dependency of this scheme that is not a stable release.

If that version ever becomes unresolvable the generator fails with a toolchain error naming it. Recovery is to move the pin to the next upstream commit whose package-lock.json resolves, re-verify that the rebuild still reproduces the published bundles, and regenerate. The committed patch keeps working the whole time — only regeneration is blocked, so this is never an outage.

Patch Path Rooting

A published tarball is rooted at the package, so an addon's patch names src/TextureAtlas.ts, not addons/addon-webgl/src/TextureAtlas.ts. Two places have to agree with that, and both fail silently if they do not:

• The checkout diff passes --relative, which must sit before the -- separator in CHECKOUT_DIFF_FLAGS. After it, git reads it as a pathspec and keeps repo-root-relative paths, and every source hunk then falls out of the emitted patch.
• git apply runs from the repo root with --directory=<packageDir>. Run from a subdirectory instead, git still resolves patch paths from the repo root, skips every hunk, and exits 0. The generator guards this by failing when applying a source patch leaves the checkout unchanged.

Version Bumps

Upstream publishes each package only when its own output changes, so the four packages carry different beta numbers while sharing one commit — at the time of writing @xterm/xterm@6.1.0-beta.303 and @xterm/headless@6.1.0-beta.302 are both built from d3e32b3. Match on package.json.commit, never on the version string; xterm-user-scrolling-contract.test.ts asserts that pairing for headless and core.

Bumping @xterm/xterm is:

1. Update the version in package.json and run pnpm install.
2. Rename both patch files to the new version and update patch, sourcePatch, and version in xterm-upstream.json.
3. Update upstream.commit to the commit field of the new tarball's package.json, and toolchain to whatever the new package-lock.json resolves.
4. node config/scripts/regenerate-xterm-patches.mjs --write.
5. pnpm install, then --check. On a bump the lockfile has no entry under the new key yet, so --write reports the gap and leaves the hash to pnpm install; --check is what proves the two agree afterwards.

Step 4 is where a real upstream conflict shows up: git apply of the source patch fails against the new tree. Resolve it in the checkout, re-diff, and rerun. The bundle hunks need no attention at any point.

Why Not Vendor a Fork

A vendored @xterm/xterm fork removes the patch entirely, but it moves Orca off the published package, so every upstream beta becomes a merge rather than a version bump, and Orca inherits responsibility for building and publishing a package it does not own. The patch is four small source hunks against a commit that reproduces byte for byte; a fork is a much larger standing cost for the same result.

Why Not Handle Composition at Runtime

CompositionHelper hooks four private call sites upstream of onData, and SortedList has no public surface at all. There is no supported extension point that reaches either, so a runtime shim would mean reaching into _core internals that upstream renames freely between betas. The patch is the smaller risk.

CI Contract

xterm_patch_sync in .github/workflows/pr.yml runs regenerate-xterm-patches.mjs --check on every PR and is part of the verify aggregate. It clones the pinned commit, installs upstream's toolchain, builds twice, and byte-compares the result against the committed patch. Both builds and the diff together are about eight seconds; npm ci for upstream's toolchain is what the job actually spends its minutes on, and the cache key is the manifest.

config/scripts/regenerate-xterm-patches.test.mjs covers the pure pieces — pnpm's diff flags and normalization, hunk splitting, round-trip stability, the commit and build-order assertions, and lockfile coupling — with no network and no build, so they run in the ordinary test shards.

Known Gaps

@xterm/addon-ligatures is still patched by hand, and can stay that way: the patch is a fifteen-line package.json edit that repoints module and adds an exports block, touching no bundle and no sourcemap. Nothing about it is generated, so there is nothing for this harness to verify.

The addons were folded into this manifest on 2026-08-29. Before that they were hand-edited minified bundles carrying a literal /* PATCH(orca): ... */ comment inside minified code, parser round-trip artifacts (!0 printed back as true, locals renamed i → i5), and no .map hunks at all — so both shipped sourcemaps whose offsets did not match the bundle beside them. All four @xterm/addon-webgl artifacts and all four @xterm/addon-serialize artifacts now reproduce byte for byte from the pinned commit, which is what closed it.

The one thing still unproven is that this holds across upstream revisions rather than at this commit. addon-serialize.js.map did not reproduce on the first attempt here; the cause was a stale out/ from a wrong build order, not upstream nondeterminism, and it reproduced exactly once the root build ran first. Treat a future non-reproducing artifact as a build-order bug until proven otherwise.