deps(frontend): upgrade to TypeScript 7 (land PR #383)

[WalksWithASwagger]

Summary

Land the Dependabot bump of typescript from 5.9.3 to 7.0.2 in frontend/ (PR #383), resolving any new type errors so the test gate passes.

Context

• Roadmap phase: phase-1.
• GitHub dependencies: blocked by fix(ci): remediate brace-expansion high-severity frontend audit failure #386. Companion Dependabot PR: build(deps-dev): bump typescript from 5.9.3 to 7.0.2 in /frontend #383.
• Relevant files: frontend/tsconfig*.json, all frontend/src/**/*.ts(x), frontend/package.json.
• Current behavior: major TypeScript jump (5.x → 7.x) can surface new/stricter type errors and changed compiler defaults.
• Desired behavior: frontend typechecks cleanly under TS 7 with the bump merged and test green.

Implementation Notes

• Rebase PR build(deps-dev): bump typescript from 5.9.3 to 7.0.2 in /frontend #383 on top of fix(ci): remediate brace-expansion high-severity frontend audit failure #386, run the typechecker, and fix new diagnostics at the source (avoid blanket any/@ts-ignore).
• Review tsconfig for options whose defaults changed across the major.

Acceptance Criteria

• typescript resolves to 7.0.x (devDependency).
• tsc/frontend typecheck passes with no new suppressions beyond justified ones.
• Frontend build + tests pass; PR test check green.

Tests/Evals

• Frontend typecheck + build + existing tests (this is the regression surface).

Verification

• npm --prefix frontend ci && npm --prefix frontend run build
• Confirm PR test check green before merge.

Agent Instructions

• Branch: deps/typescript-7 (or update PR build(deps-dev): bump typescript from 5.9.3 to 7.0.2 in /frontend #383's branch).
• Scope to type-error resolution; no feature or lint-rule churn.

Out of Scope

• ESLint/globals bumps (build(deps-dev): bump globals from 15.15.0 to 17.8.0 in /frontend #382) and other deps.

Human Checkpoints

• None beyond normal review + test gate.

[github-actions]

Agentic dev loop started on branch codex/issue-388-deps-frontend-upgrade-to-typescript-7-land-pr-38 with provider noop.

[github-actions]

Agentic dev loop finished without opening a PR. Status: no-pr. Provider: noop.

[WalksWithASwagger]

Blocked: TS 7 breaks the lint toolchain — needs a scope decision

Attempted the bump (typescript ^5.8.3 → ^7.0.2 in frontend/package.json, lockfile regenerated with npm@10). TypeScript 7.0.2 is now the latest npm release — the native (Go) port; it pulls in the platform-binary optional deps @typescript/typescript-* (why the lockfile diff is large). The bump itself is trivial, but the test gate cannot go green within this issue's declared scope. Three independent blocks:

1. npm ci fails on peer resolution. No released typescript-eslint allows TS ≥ 6.1:

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

typescript-eslint@latest is 8.65.0 (peer typescript >=4.8.4 <6.1.0); even canary/8.65.1-alpha.7 still caps <6.1.0. --package-lock-only "succeeds" only by overriding peers with warnings; strict npm ci (what CI runs) rejects it.

2. lint is hard-blocked by typescript-eslint itself. Even if peers are forced, eslint . throws at load time:

typescript-eslint does not support TS 7.0.
Please see .../announcing-typescript-7-0/#running-side-by-side-with-typescript-6.0
See also https://github.com/typescript-eslint/typescript-eslint/issues/10940

This is a deliberate runtime guard. Their only supported workaround today is running typescript-eslint against a side-by-side TS 6 API (install typescript@6 alongside for the linter). TS ≥ 7.1 support is tracked but unreleased.

3. Three real TS 7 typecheck errors (fixable at source, but moot until #1/#2 are resolved):

src/components/generate-status.test.tsx(1,10): TS2305: '@testing-library/react' has no exported member 'fireEvent'
src/components/generate-status.test.tsx(1,29): TS2305: '@testing-library/react' has no exported member 'screen'
src/routes/library.index.tsx(44,19): TS2322: SearchMiddleware<...> generic variance (TanStack Router types)

Why this needs a human

This issue scopes out "ESLint/globals bumps (#382) and other deps," yet the only path to a green test gate under TS 7.0 requires changing the lint toolchain (side-by-side TS 6 for typescript-eslint, or dropping/reconfiguring the lint step) plus a typescript-eslint bump that does not yet exist. Forcing it with --legacy-peer-deps/overrides would ship a lint gate that throws.

Options for the maintainer

• Hold until typescript-eslint ships TS ≥ 7.1 support (issue #10940), then land the bump + fix the 3 type errors. (Recommended — lowest risk, keeps scope clean.)
• Adopt the side-by-side TS 6 API for typescript-eslint now (new dep + config), expanding scope beyond this issue.
• Land TS 7 while temporarily decoupling lint from the test gate (explicit, tracked as its own decision).

Dependabot PR #383 (raw bump) hits the same wall. Not opening a superseding PR — validation cannot pass. Branch codex/issue-388-typescript-7 holds the bump + regenerated lockfile locally for whoever picks a path. Adding needs-human.