Refactor Decopilot worker contract

[tlgimenes]

Summary

• Narrows the desktop link worker contract to a v3 single-message harness input with explicit harness.sessionId, repo/no-repo cwd semantics, and protocol-version rejection with upgrade guidance.
• Keeps Decopilot context/history loading inside the Decopilot implementation and removes unsupported desktop Decopilot runtime registration.
• Moves shared CLI helpers out of Decopilot-specific modules and adds contract coverage for desktop CLI image work items.

Test Plan

• bun test packages/sandbox/daemon/routes/dispatch.test.ts packages/sandbox/dispatch/schemas.test.ts packages/sandbox/daemon/rebase-workspace-cwd.test.ts packages/harness/src/workspace-cwd.test.ts
• bun run check

Notes

• Full Playwright e2e execution was previously blocked locally by missing NATS on 127.0.0.1:4222 / ::1:4222.
• Live Chrome DevTools smoke against the provided app URL was blocked by that browser context redirecting to /login.

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Summary by cubic

Moves Decopilot and CLI harnesses to link protocol v3: one userMessage, resume via harness.sessionId, and runId moved to the dispatch envelope. Removes the desktop Decopilot runtime, tightens workspace.cwd to null or /repo, and enables vision on CLI models for image inputs.

• Migration

  • Upgrade the desktop link: run bunx decocms@latest link (v3 required; stale links show an upgrade message).
  • Send a single userMessage (no messages array); resume via harness.sessionId (not resumeSessionRef).
  • Set workspace.cwd to only null or /repo; the daemon rebases /repo and passes through null.
  • Put runId in the dispatch envelope (outside harnessInput); the daemon returns 400 missing_run_id when absent.
  • Decopilot is cluster-only; the desktop runtime is removed and the @decocms/harness ./decopilot export is gone.
  • Provide capabilities: { vision: true, text: true } on CLI models to accept image file parts.

• Refactors

  • Added setDecopilotRunContext/requireDecopilotRunContext to carry Decopilot-only context (MCP, model sources, object storage, branch, user, prior messages) off the wire and load history in-cluster.
  • Moved shared helpers to @decocms/harness root (stream-error, current-context-prompt, thread-title, title-generator) and updated imports.
  • Updated claude-code and codex to v3: accept one userMessage, forward harness.sessionId, support image file parts, and stay decoupled from the Decopilot namespace.
  • Tightened sandbox dispatch: rebases symbolic cwd, enforces the v3 input schema, and exposes a link upgrade message; emits missing_run_id for bad envelopes.
  • Added tests for link-pull image parts, CLI isolation/import boundaries, v3 work items, and cwd rebasing; updated schemas/fixtures to the v3 contract.

^{Written for commit b74a0fd. Summary will update on new commits.}