Harden browser response boundaries

[parsakhaz]

Summary

• isolate the web fallback Discord window from its opener
• branch on remote-daemon HTTP status before decoding success or error payloads
• separate notebook JSON text formatting from the component sanitized HTML render paths

Part of #403.

React Doctor

• current-main baseline: 0 errors, 317 warnings, 317 total
• after: 0 errors, 314 warnings, 314 total
• removes window-open-without-noopener, no-fetch-response-used-without-status-check, and the false-positive unsafe-json-in-html finding without replacements

Validation

• pnpm lint
• pnpm typecheck
• pnpm --filter frontend test (245 tests)
• pnpm build (including signed universal DMG/ZIP packaging)
• pnpm dlx react-doctor@0.9.2 frontend --no-score --no-supply-chain --no-dead-code --json

Automated QA

• Status: pass at 4c4017cb
• Remote invoke transport: 42/42 focused tests passed across browser, main client, and HTTP server, including non-JSON 401 and malformed 200 responses.
• Notebook JSON boundary: server-render proof confirms script-like JSON is emitted as escaped text, with no raw script element.
• Full gates: 267/267 frontend tests, root typecheck, root lint, and React Doctor all passed. React Doctor reported 0 errors and 315 warnings on current main; none are the three boundary findings addressed by this PR.
• Screenshots: omitted because the UI changes have no intended visual delta.
• Remaining human check: optionally open the Discord fallback in web mode and inspect that the new tab has no opener.

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[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 4c4017c.}

[parsakhaz]

Verdict: Request changes - HTTP failure classification still depends on decoding the response body. GitHub does not permit the PR author to submit a REQUEST_CHANGES state, so this formal review is posted as COMMENT with a blocking Must-Fix.
Counts: Must Fix: 1 (security: 0) · Should Fix: 0 · pass 1/3

Must Fix

• MF-1 - Classify failure status before requiring a JSON error payload · frontend/src/remote/runtime/remoteDaemonBrowserClient.ts:126 · derive auth and retry behavior from response.status first, then parse an optional server message on a best-effort basis · violates the PR intent to branch on remote-daemon HTTP status before decoding payloads
  • Evidence: lines 126-132 await response.json() before the 401/403 branch. A non-JSON response throws into the generic catch at line 147, so status classification is skipped.
  • Failure scenario: a reverse proxy or incompatible remote host returns 401 with an HTML or empty body; invoke retries four times and finally exposes a JSON parse error instead of stopping immediately with the invalid connection-code guidance.

Praise

• frontend/src/components/DiscordPopup.tsx:81 isolates the fallback window with noopener,noreferrer.
• frontend/src/components/panels/editor/NotebookPreview.tsx:115 keeps notebook JSON formatting in React text content while DOMPurify remains limited to HTML and SVG render paths.

Checks run: pnpm typecheck; pnpm lint; pnpm --filter frontend test (266 passed); main/src/daemon/remotePwaBrowserRuntime.test.ts passed during the main Vitest run.

[parsakhaz]

Deep refactor Follow-ups

• Consolidate browser and main-process retry/status policy only after adding a shared cross-runtime failure matrix for 408, 401/403, 429, 5xx, malformed JSON, and aborted requests.
• Validate daemon command results as JSON-safe values before HTTP serialization. The server registry currently returns unknown, and tightening that boundary needs broader command coverage.
• Add focused notebook sanitizer tests for hostile HTML and SVG payloads. This pass proves the JSON text path, while the existing DOMPurify paths remain unchanged.

[parsakhaz]

Three-pass review complete

Review

• Rebased the PR onto current main.
• Found one Must-Fix: auth and non-retryable status handling still depended on parsing a JSON body.
• Fixed it in ff8e8253 and added coverage proving an HTML 401 stops after one request and returns connection-code guidance.
• The formal review is COMMENT because GitHub does not allow an author to request changes on their own PR.

Simplify

• f2b79748 removes the redundant RequestInit spread and success else branch.
• MIME string and line-array decoding now uses the existing union schema once.
• DiscordPopup and the regression fixture were reviewed but left unchanged because further abstraction would add indirection.

Refactor

• 4c4017cb moves the invoke success/error envelope and BoundarySchema into the shared remote-daemon contract.
• The HTTP server, main client, and browser client now consume one response definition.
• The browser now runtime-decodes successful envelopes instead of trusting a TypeScript assertion.
• Added tests for malformed 200 envelopes and escaped notebook JSON text.

Validation

• pnpm typecheck
• pnpm lint, including zero advisory anti-slop findings and passing boundary conformance
• pnpm --filter frontend test: 267/267
• focused remote transport suites: 42/42
• React Doctor 0.9.2: 0 errors, 315 warnings on current main; none are the three boundary findings addressed by this PR
• No screenshots because there is no intended visual change

Left for parsa

• Wait for the newly triggered GitHub checks, which are currently in progress.
• Optionally verify the Discord web fallback manually and inspect that the new tab has no opener.
• Review the separate Follow-ups comment, then merge when satisfied. I did not merge.