fix: harden provider trust boundaries

[TheStreamCode]

Summary

Hardens the extension at its external trust boundaries and fixes the VS Code compatibility contract discovered during the repository audit.

Changes

• Propagate model-list cancellation, make cache invalidation generation-safe, and reserve model-router for the virtual Auto model.
• Fail closed on malformed, oversized, incomplete, or unavailable streamed tool calls.
• Bound model/account/error/SSE payloads and quota fallback fan-out; use limited fallback concurrency.
• Treat unsafe model-filter regexes literally and harden quota normalization against negative and mixed unlimited values.
• Raise the minimum VS Code version to 1.106, pin matching API types, and update vulnerable transitive packaging dependencies.
• Add offline regressions and synchronize README, guides, contributor instructions, agent guidance, settings copy, and changelog.

Verification

• npm run check passes (43 offline tests, lint with zero warnings, production bundle, VSIX contents)
• Manually verified in Extension Development Host, or not applicable (network/UI behavior is covered by injected offline clients and pure regressions)
• Added or updated regression tests for behavior changes
• Updated user documentation and CHANGELOG.md, or not applicable
• No new outbound endpoints, or each new endpoint is documented
• npm audit --omit=dev reports zero vulnerabilities
• Packaged VSIX contains only the allowlisted extension files

Privacy

No new endpoints or data flows. Existing responses are now read with explicit limits, cancellation is propagated through model-list and account requests, and API-provided tool calls are validated before exposure to VS Code.

Notes

• Local VSIX SHA-256: EBB1D22BDEF213B39483FDE9DF8A347400B629C5BB01E32DC4316B65730E35EB.
• No live Chutes tests were run; they require CHUTES_KEY and can make billable-capable requests.
• No version bump, tag, GitHub release, Marketplace publish, or Open VSX publish is included.