feat(sdk): add shared codex runtime strategy foundation

[yaniv-tg]

Summary

This PR moves the first Codex runtime uplift into the shared SDK instead of continuing to grow duplicated plugin-only logic.

It adds shared runtime foundations for:

• harness capability reporting
• model routing defaults for plan / interactive / execute / review / fix
• execution strategy resolution for local, subagent, and future cloud modes
• dispatch envelope abstraction
• orchestrator_task metadata for subagent fan-out
• waiting-iteration metadata exposing routed models, pending effects by mode, and harness capabilities

This is PR 1 of the Codex upstreaming work. It is intentionally limited to shared SDK/runtime foundations.

What Changed

Shared runtime modules

Added:

• packages/sdk/src/runtime/capabilityReport.ts
• packages/sdk/src/runtime/modelRouting.ts
• packages/sdk/src/runtime/executionStrategy.ts
• packages/sdk/src/runtime/strategyDispatch.ts

These provide:

• Codex capability detection in shared SDK code
• default model routing:
  • interactive -> gpt-5.3-codex-spark
  • other phases -> gpt-5.3-codex
• strategy resolution:
  • local
  • subagent
  • cloud requested but still local fallback in this PR
• dispatch envelope generation for runtime consumers

Runtime wiring

Updated:

• packages/sdk/src/runtime/intrinsics/task.ts
• packages/sdk/src/runtime/intrinsics/orchestratorTask.ts
• packages/sdk/src/runtime/orchestrateIteration.ts
• packages/sdk/src/runtime/types.ts
• packages/sdk/src/runtime/index.ts

This adds:

• executionHints on pending effect actions
• iteration metadata for:
  • harnessCapabilities
  • routedModelsByPhase
  • pendingEffectsByMode
• shared handling of orchestrator-task execution metadata

Task schema updates

Updated:

• packages/sdk/src/tasks/types.ts
• packages/sdk/src/tasks/kinds/index.ts

This extends orchestrator_task definitions with:

• executionMode
• modelPhase
• parallelism
• subtasks

This is the baseline needed for local subagent fan-out semantics in shared code.

Tests

Added/updated:

• packages/sdk/src/runtime/__tests__/strategyRuntime.test.ts
• packages/sdk/src/runtime/__tests__/intrinsics.behaviors.test.ts
• packages/sdk/src/runtime/__tests__/orchestrateIteration.integration.test.ts
• packages/sdk/src/tasks/__tests__/kinds.test.ts

Coverage includes:

• Codex capability reporting
• interactive model routing defaults
• cloud fallback behavior for PR 1
• subagent dispatch envelope generation
• orchestrator-task metadata propagation
• waiting-iteration metadata for routed model + execution mode

Docs

Updated:

• README.md
• plugins/babysitter-codex/README.md

These now point out that shared Codex runtime policy is moving into packages/sdk.

Non-goals in This PR

This PR does not yet do:

• real cloud submit/resume integration
• deferred cloud lifecycle handling
• shared instruction deduplication across plugin docs/skills
• deletion of the duplicated plugins/babysitter-codex tree

Those should follow in later PRs.

Validation

Ran:

npm.cmd test -- --run src/runtime/__tests__/strategyRuntime.test.ts src/runtime/__tests__/intrinsics.behaviors.test.ts src/runtime/__tests__/orchestrateIteration.integration.test.ts src/tasks/__tests__/kinds.test.ts src/harness/__tests__/harness.test.ts

Result:

• 5 test files passed
• 63 tests passed
• 0 failed