Closes #35016.

Summary

Replaces ambiguous V2 execution settlement and retry events with explicit lifecycle, bounded retries, and a closed structured error contract.

• Adds durable session.execution.started, .succeeded, .failed, and .interrupted events.
• Adds durable session.retry.scheduled and projects retry state into one Assistant across attempts.
• Introduces the closed SessionStructuredError wire union with dot-cased type discriminators.
• Preserves permission and typed tool failures through tool, step, and execution settlement.
• Maps content-filter to visible failed state instead of an empty successful Assistant.
• Types finish reasons with the shared browser-safe provider set.
• Derives TUI status and notifications from execution lifecycle events.
• Updates V2-backed run compatibility consumers to the explicit lifecycle.

Execution lifecycle records are historical observations of one process-local coordinator busy period. They carry no execution identity, do not define transcript boundaries, and replay never implies current liveness or recovery. /session/active remains the current-liveness authority.

Retry Policy

• Maximum five total LLM calls.
• Retries only pre-output rate-limit, provider-internal, and transport failures.
• Authentication, quota, content policy, invalid request/output, route, and unknown-provider failures are terminal.
• Midstream output and tool execution are never retried.
• Provider retry-after delay wins over 2-second exponential backoff.
• Every llm.stream call remains one step and consumes the agent step allowance.
• All attempts reuse one projected Assistant; retry state clears on the next attempt or terminal lifecycle event.

Persistence

20260703210000_reset_v2_execution_errors clears V2 events, sequences, projected messages, and admitted inputs. New durable contracts start at version 1.

Verification

• Schema: 14 focused tests
• Core: 154 focused tests
• TUI: 33 focused tests
• Run compatibility: 40 focused tests
• Client: 16 focused tests
• SDK typecheck and generated-surface test passed
• All affected package typechecks passed
• Full-repo pre-push typecheck passed
• Client and legacy SDK generators reproduced cleanly on consecutive runs
• Migration sync check passed
• Prettier clean; file-scoped oxlint has 0 errors
• Two focused independent re-reviews passed after retry, interruption-race, structured-error, and TUI-bootstrap corrections

packages/client/test/contract-identity.test.ts remains a parent-branch baseline failure because the client package does not declare its test-only @opencode-ai/core dependency; the other client tests pass.