Fix runtime cancellation state and stop controls / 修复运行取消状态与停止控制

[SivanCola]

Closes #4404
Closes #4107
Closes #3411
Addresses #4066 (the uninterruptible bash process-tree path)

Related: #4522 repairs stale prompt replay after frontend reconciliation. This PR is complementary: it fixes the authoritative runtime/cancel contract and makes Stop reachable while the turn is waiting for approval or ask input.

Summary

• Added a structured controller runtime snapshot with running, pendingPrompt, backgroundJobs, cancelRequested, and cancellable.
• Made Cancel() idempotently mark cancellation immediately, clear pending approval/ask prompts, and still settle through the normal turn completion path.
• Switched desktop tab/runtime metadata to the backend-authoritative snapshot so sidebar/chrome guards and composer state no longer disagree.
• Kept Stop reachable during approval and ask prompts, including Esc handling inside those pending-decision surfaces.
• Added regression coverage for approval cancellation, ask cancellation, desktop runtime metadata, frontend runtime reconciliation, and Windows bash child-process tree cancellation.

Verification

• go test ./internal/control
• (cd desktop && go test .)
• (cd desktop/frontend && npm run typecheck)
• (cd desktop/frontend && npm run test:typecheck)
• (cd desktop/frontend && npm test)
• Windows cross-compile of the ./internal/tool/builtin test package passed.
• go test ./internal/tool/builtin -run 'TestBashCancelReturnsPromptly|TestReapTreeKillsGroupStragglers' -count=1
• go test ./internal/provider/openai -run TestStreamStallTimesOut -count=1
• go test ./internal/agent -run TestRunCancelledMidStreamLeavesResumableSession -count=1
• go test ./... -skip 'TestSandboxEnforcesWrites|TestBashSandboxConfinement'

The skipped root-suite cases are the existing macOS sandbox-enforcement checks that fail independently in this local environment; the cancellation/runtime changes and focused suites passed.

[SivanCola]

@codex review

[chatgpt-codex-connector]

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[SivanCola]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. What shall we delve into next?

Reviewed commit: 0a01ccde99

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