deps(frontend): TypeScript 7 (lands #383, issue #388)

[WalksWithASwagger]

What

Bumps the frontend typescript devDependency from ^5.8.3 to ^7.0.2.

• Tracked by deps(frontend): upgrade to TypeScript 7 (land PR #383) #388.
• Supersedes Dependabot build(deps-dev): bump typescript from 5.9.3 to 7.0.2 in /frontend #383 (same bump, 5.9.3 → 7.0.2), which currently fails CI. Please do not merge build(deps-dev): bump typescript from 5.9.3 to 7.0.2 in /frontend #383 in favor of this PR; leave both open for a maintainer decision.
• Diff is intentionally minimal: only frontend/package.json and frontend/package-lock.json.

Honesty up front: CI is RED and this is not cleanly mergeable yet

This is the riskiest item in the dep batch (a two-major TS jump to the new native/Go port). The bump itself is clean, but the repo's lint toolchain does not support TypeScript 7 yet, and that is not fixable with a surgical, in-scope change. Landing this as-is would knowingly break the test gate. Filing it review-ready so a human can decide.

What passes vs. fails (verified locally, Node 26)

Check	Result	Notes
tsc --noEmit (typecheck)	✅ PASS	Native tsc@7 compiles the source cleanly, no type errors.
vite build	✅ PASS	Builds .output/ fine; vite/rollup/esbuild don't need the TS JS API.
vitest run (test)	✅ PASS	10/10 tests pass.
npm ci (CI install step)	❌ FAIL	Strict ERESOLVE peer conflict (see below).
eslint . (lint)	❌ FAIL	typescript-eslint hard-refuses TS 7.0 at runtime (see below).

CI's test job runs npm --prefix frontend ci then npm run verify (which chains frontend typecheck && test && build && lint). It will fail at the install step first, and would fail at lint even if install were forced.

Root cause (single upstream issue, two symptoms)

typescript-eslint@8.65.0 declares peer typescript: ">=4.8.4 <6.1.0", which TypeScript 7 violates, and it also throws at runtime:

typescript-eslint does not support TS 7.0.
Please see https://devblogs.microsoft.com/typescript/announcing-typescript-7-0/#running-side-by-side-with-typescript-6.0
to run typescript-eslint using the TS 6 API.
See also https://github.com/typescript-eslint/typescript-eslint/issues/10940 for tracking typescript-eslint's support for TS >=7.1

1. Install fails — npm ci (strict peers) errors:

   Conflicting peer dependency: typescript@6.0.3
   peer typescript@">=4.8.4 <6.1.0" from typescript-eslint@8.65.0
   

   (npm install only downgrades this to a warning; npm ci, which CI uses, is strict.)
2. Lint fails — even past install, eslint . throws typescript-eslint does not support TS 7.0.

Additional context: the typescript@7 npm package is the native Go port — it ships only a native tsc binary (no tsserver) and no longer exports the JS compiler API at the main entry ("." → lib/version.cjs; the real API moved to ./unstable/*). Tools that require('typescript') for the classic API (typescript-eslint) therefore break.

Why I did not "fix" it

Per the task's guardrails (no blanket any/@ts-ignore, no unrelated dep bumps, change only what TS7 requires): there is no released typescript-eslint that supports TS 7.0 (support is tracked for TS >=7.1 in typescript-eslint#10940). Every real workaround is out of scope for a surgical bump. Deliberately left for maintainer decision.

Options for a maintainer

• A. Hold (recommended). Keep TypeScript at 5.9.x until typescript-eslint ships TS 7.x support (typescript-eslint#10940), then revisit. Lowest risk.
• B. TS6-API side-by-side. Adopt the MS-documented pattern (run typescript-eslint against a co-installed typescript@6, use typescript@7's tsc for typecheck). Architectural change beyond a dep bump; would need its own issue.
• C. Degrade the lint gate. Add .npmrc legacy-peer-deps=true and drop typescript-eslint / TS-aware lint. Makes CI green but weakens the lint gate — not recommended.

Verification commands run

npm --prefix frontend install      # regenerated lockfile (ERESOLVE warnings)
npm --prefix frontend run typecheck # PASS
npm --prefix frontend run build     # PASS
npm --prefix frontend run test      # PASS (10/10)
npm --prefix frontend run lint      # FAIL — typescript-eslint refuses TS 7.0
npm --prefix frontend ci            # FAIL — ERESOLVE peer conflict

Refs #388. Supersedes #383. Do not merge until the lint-toolchain blocker is resolved.

🤖 Generated with Claude Code

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