[TheGreatAxios]

Two defects

1. Shared tsbuildinfo clobbers itself. The combined tsconfig.json (the file bare tsc, ESLint's projectService, and editors discover by convention) extends tsconfig.src.json, inheriting tsBuildInfoFile: "dist/tsconfig.tsbuildinfo". The composite tsc --build and the combined --noEmit check both write that same file, so each invalidates the other's incremental state on every run. Fix: COMBINED_COMPILER_OPTIONS in scripts/generate-tsconfig-references.ts now sets tsBuildInfoFile: "tsconfig.tsbuildinfo", landing next to the package's tsconfig.json (already gitignored via *.tsbuildinfo). combinedFieldsMatch already iterates Object.keys(COMBINED_COMPILER_OPTIONS), so drift detection picks the new key up for free. Regenerated every tsconfig.json with bun run scripts/generate-tsconfig-references.ts. The vendored vendor/intx/*/tsconfig.json files are generator output too, so their content hashes in scripts/checks/kill-dates.txt are updated in the same change.

2. CI caches nothing for typecheck. The typecheck job in .github/workflows/ci.yml only restores node_modules via setup-workbench, so every PR pays the full cost from a cold cache. Added an actions/cache@v4 step keyed on bun.lock, .bun-version, tsconfig.base.json, scripts/generate-tsconfig-references.ts, and github.sha, with a restore-keys prefix so a PR falls back to the newest matching cache (typically main's). Paths are listed per workspace root (apps/*/dist, packages/*/dist, ...) rather than **/dist/**: the recursive glob walks node_modules and follows every workspace symlink in it, and the save step ran for over 40 minutes before it was cancelled. With explicit roots the ~200 MB cache saves in 2s.

CI timings, bun run typecheck step on this branch

run	cache	step	job total
33877407144	not found (seeds it)	457s	8m03s
33878262756	restored	174s	~3m20s

Baseline on main before this change: 416s to 446s step, 7m14s to 7m50s job.

What remains in the warm 174s is the 113 per-project tsc -p --noEmit invocations each re-reading their program on a 4-core runner even when buildinfo says nothing changed. Further cuts mean fewer projects (CL-7249) or a larger runner.

Local timings (this worktree)

• bun run typecheck run 1 (tsconfigs just regenerated, effectively cold): 45.1s wall
• bun run typecheck run 2 (warm): 11.4s wall
• bunx tsc --build tsconfig.build.json immediately after: 0.33s (previously 13.5s, confirming defect 1 is fixed)

Touch-test (does tsc --build skip on fresh mtimes?)

TypeScript 6.0.3. After a warm build, touched every .ts file under packages/ and apps/ (mtime only), then ran tsc --build tsconfig.build.json: 2.5s wall on the first run (partial recompute, not the ~15s cold build; the content-hash check short-circuits most files even though --build's up-to-date check uses mtimes), 0.94s on the second. The per-project --noEmit checks use --incremental content hashes and do not care about mtimes at all.

[linear-code]

CL-7415

[TheGreatAxios]

Self-review

Rebased onto main (conflicts were only in scripts/checks/kill-dates.txt), regenerated tsconfigs and recomputed vendor hashes, fixed one confirmed cache-coverage gap, and verified the fix's own claims (near-instant repeat tsc --build).

• CONFIRMED-FIXED: test/isolation/tsconfig.json is a real incremental project (scripts/typecheck.ts runs tsc -p test/isolation/tsconfig.json --noEmit, base config has incremental: true) that writes a 483 KB test/isolation/tsconfig.tsbuildinfo, but the cache path: list only had test/tsconfig.tsbuildinfo, not test/isolation/tsconfig.tsbuildinfo. That project always recompiled cold on every CI run regardless of cache hits. Added the missing path.
• CONFIRMED-FIXED: branch was CONFLICTING against main — rebased, resolved the kill-dates.txt hash conflict by recomputing every vendor/intx/* hash with hashDirectory directly (.tsbuildinfo files are already excluded from the hash by scripts/checks/lib/tree-hash.ts, so the tsBuildInfoFile rename doesn't itself change any hash — the diff is just this branch's own tsconfig.json regeneration for vendor/intx/db plus main's independent hash updates for the rest).
• DISMISSED: cache path list vs package.json workspaces globs — templates is a workspace but is intentionally excluded from scripts/typecheck.ts's PROJECT_GLOBS (never globbed, no dist/tsbuildinfo produced), so its absence from the cache path list is correct, not a gap. The listed roots (apps/*, packages/*, tools/*, workflows/*, vendor/intx/*) match PROJECT_GLOBS exactly.
• DISMISSED: .gitignore already covers the new tsconfig.tsbuildinfo location via the existing *.tsbuildinfo glob — no change needed.
• DISMISSED: cache key/restore-keys — key includes github.sha for exact-commit caching, restore-keys drops the sha for prefix fallback to the newest matching cache (main's, typically) as the PR body's timing table confirms. Correct.
• DISMISSED: generator drift check — combinedFieldsMatch iterates Object.keys(COMBINED_COMPILER_OPTIONS), which now includes tsBuildInfoFile, so drift is caught for free as claimed. Verified by reading scripts/generate-tsconfig-references.ts.

Targeted tests: bun run scripts/checks/killdates.ts (pass), bun run typecheck (pass, ~10-16s locally after regeneration — a local node_modules install anomaly for cronstrue unrelated to this diff needed a manual workaround to verify, not part of the PR), bunx tsc --build tsconfig.build.json twice (0.33s / 0.32s, confirms defect 1 stays fixed after rebase).

Conflict risk: PR #632 ("re-pin Interchange vendor + sidecar modules") also touches scripts/checks/kill-dates.txt — expect another rebase/hash-recompute pass on whichever of these two merges second.