[codex] Direct Roslyn delivery, Serena retirement and E4 checkpoint

[linnnn89]

WinCode now defaults to its local text provider and uses a directly configured Roslyn Code Host for semantic queries. This draft saves the current engineering iteration, including the in-progress E4 error contract migration.

Changes

• Retire the external Serena adapter, launchers and protocol-only fixtures; migrate the text source to local-text in the 0.13.0 contract.
• Correct impact file/project identity and bounded Roslyn evidence handling; propagate selected symbolLocation into impact and refactoring.
• Track compilation-related inputs plus explicitly configured additionalInputs, preserving encoding and stale-snapshot rejection.
• Publish and inventory Code Host/Roslyn/BuildHost sidecars, check build identity, share installed SDK selection and add real Roslyn acceptance to Node 22 CI.
• Separate workspace discovery, local text scanning, cache fingerprinting, context coverage, UIA Host responsibilities and verification scenarios; split historical mixed test suites and synchronize repository guides.
• Start E4: errors return JSON text and matching structuredContent; preserve UI/trash domain outcomes and workspace recovery state. This part still needs dedicated regression coverage and final manual reconciliation.

Current validation

• Latest npm run check: typecheck, Gateway and .NET builds passed; core regression 306/307, with one failure in tests/resource-cleanup.test.ts: an in-place modification to a Chinese-named file did not change the workspace fingerprint. Root cause is not yet established. The check stopped before stdio and delivery stages.
• npm run test:error-contracts: 10 scenarios passed on this E4 implementation.
• Prior to E4, the iteration passed core 307/307, desktop 35/35, Host 58 scenarios, real MCP 19 scenarios and a 70-call mixed load check. These earlier results are not full validation of this checkpoint.
• Staged whitespace checks passed. Local dependencies, generated binaries, caches and test evidence directories are excluded from the commit.

Remaining before merge

Investigate the fingerprint regression, finish E4's error/recovery coverage and guide verification, then rerun the required checks. Remote CI results and actual client activation remain separate gates. No changes were made to the user's active client configuration or global Skill installation.

Detailed decisions and local report references are recorded in docs/codex_worklog.md.