[dependabot-agent] Fix undici vulnerabilities via npm override

[cao-githubnext-gh-aw-cao-write]

What changed

• Package/ecosystem: npm (root package.json)
• Manifest(s): package.json, package-lock.json
• Old version: undici transitively resolved to 5.29.0/mixed sub-6.28.1 versions across @actions/artifact, @actions/github, @actions/http-client, @github/local-action
• New version: undici pinned to ^6.28.1 everywhere via a top-level npm overrides entry (no direct dependency version change)
• Update type: security (transitive override, no direct package version bump)

Why now

npm audit reports 5 vulnerabilities (4 moderate, 1 high) rooted in transitive undici copies pulled in below 6.28.0 by @actions/artifact, @actions/github, @actions/http-client, and @github/local-action (all devDependencies used only for local Action testing/tooling). The highest-severity issue (CVSS 7.5) is an unbounded WebSocket permessage-deflate memory-consumption DoS (GHSA-vxpw-j846-p89q), plus several HTTP smuggling/CRLF/cookie-injection issues fixed between undici@6.24.0–6.28.0.

A prior PR (#10838) applied this identical fix but was closed without merging, so the vulnerability remains unresolved on main. Re-verified with a fresh npm audit before recreating this change.

Risk assessment

• Runtime/dev/build/CI scope: dev-only. undici is not a direct dependency; it is pulled in transitively by @actions/artifact, @actions/github, @actions/http-client, and @github/local-action, all devDependencies used for local Action testing/tooling, not the Astro docs build or dashboard runtime.
• Direct/transitive: transitive (2–3 levels deep); fixed via a top-level overrides pin rather than bumping any direct dependency, avoiding the @github/local-action@5.2.0 major-version downgrade that npm audit fix --force would otherwise force.
• Reachability: no source files import undici directly; it is only exercised via the GitHub Actions SDK HTTP clients used in dev/test tooling.

Validation

• Commands run: npm install (clean install with the override), npm audit --json (0 vulnerabilities after, vs 5 before), npm run typecheck:cao (passed, no errors), npm run test:unit (350/357 pass; the 4 failures/3 cancellations were verified present identically on unpatched main before this change — unrelated pre-existing issues: activity/cao.mjs default-location tests, telemetry cache-absent tests, CAO policy resolve-policy worker-identity check, and a clean-room compilation settings test)
• Result: npm audit now reports 0 vulnerabilities (was 4 moderate + 1 high); all undici copies in package-lock.json resolve to 6.28.1.
• Remaining gaps: did not run npm run compile / npm run docs:build (no .md workflow source or docs content changed by this PR) or the dashboard site's own test suite (unaffected — separate dashboard/site/package.json, already audited clean with 0 vulnerabilities in this run).

Control Plane

• Correlation ID: 34780480700-263
• Central repo: githubnext/gh-aw-cao
• Run URL: https://github.com/githubnext/gh-aw-cao/actions/runs/34780904852

Toolchain: Node/npm as pinned by CI (no engines field declared in package.json; used the preinstalled npm in the workflow runner). Registry preflight: npm registry fully reachable, no auth issues. No breaking changes — this is an overrides pin only, no direct dependency version bump, no API surface change. Risk: low. Confidence: high (clean install, 0 audit findings, typecheck clean, no test regressions beyond pre-existing baseline failures verified on main).

Rollback: revert this commit (removes the overrides block from package.json and restores package-lock.json); no other files are affected.

Smart-Dependabot-Merge-Candidate: yes

Reviewer checklist

• CI passes
• CODEOWNERS or service owners reviewed
• Security-sensitive areas approved, if applicable
• Deployment/canary owner confirms runtime health, if needed

Rollback guidance

• Revert this PR to restore the previous transitive undici resolution.
• package.json and package-lock.json must be reverted together (lockfile was regenerated from the override).

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