feat(engine): add type: wait step for in-process pauses

[jrob5756]

Closes #218.

Summary

Adds a new type: wait step that pauses workflow execution for a parsed duration via asyncio.sleep. Pure in-process, cross-platform, no shell sleep dependency. Composes with routing loop-backs for polling, rate-limit cooldowns, demos, and external-system catch-up.

agents:
  - name: cooldown
    type: wait
    duration: 60s              # int/float seconds, "Ns/Nm/Nh/Nms", or Jinja2
    reason: "Cooling down"     # optional, shown in dashboard
    routes:
      - to: next_step

Behavior

• Duration: accepts plain int/float seconds, suffixed strings (ms/s/m/h), and Jinja2 templates. workflow.input.* available without explicit input: declaration (wait joins script/workflow in _LOCAL_RENDER_AGENT_TYPES).
• Bounds: 0 < duration ≤ 24h. Templated values defer literal validation to runtime.
• Booleans rejected pre-coercion via a mode="before" field validator — Pydantic v2 would otherwise silently accept True as int 1.
• Esc/Ctrl+G cancellation: sleep races against the engine's interrupt_event. When the interrupt wins, the wait returns early with interrupted=True without clearing the event, so the engine's between-step _check_interrupt triggers the normal interrupt menu.
• Workflow timeout: limits.timeout_seconds cancels in-flight waits via LimitEnforcer.wait_for_with_timeout (same wrapping used for scripts).
• Iteration counting: wait steps count toward limits.max_iterations (step counter). max_agent_iterations (per-LLM-agent tool counter) is not applicable.
• Public output contract (per the issue): strictly {"waited_seconds": float} in workflow context. Extra metadata (requested_seconds, reason, interrupted) lives only in event payloads.

Events

• Existing generic agent_started fires before type dispatch with agent_type: "wait", so dashboards keyed on agent lifecycle work unchanged.
• Type-specific wait_started/wait_completed/wait_failed carry the additional fields (mirrors the existing script convention exactly).
• Resume replay extends _synth_agent_or_script with a wait branch so checkpointed wait steps round-trip cleanly.

Validation

• Rejects wait inside parallel groups and as for_each inline agents.
• Forbids 22 incompatible fields on wait; forbids duration/reason on all non-wait types.

Dashboard

• New 'wait' NodeType with WaitNode (Clock icon) + WaitDetail component.
• graph-layout.ts maps wait → waitNode; node is registered in WorkflowGraph nodeTypes.
• Store carries duration_seconds, waited_seconds, requested_seconds, reason, interrupted on NodeData.
• Activity log renders Waiting Xs — reason and Wait completed (Xs) — interrupted entries.

Example

examples/wait-step.yaml — polling pattern with templated poll interval and route loop-back.

Tests

• tests/test_engine/test_duration.py — pure parser (26 cases).
• tests/test_config/test_wait_schema.py — schema validation (41 cases: valid forms, required duration, boolean rejection, bounds, every forbidden field, parallel/for_each rejection, wait-only fields on other types).
• tests/test_executor/test_wait.py — sleep accuracy, interrupt cancellation (verifies the event stays set for engine consumption), templated durations, runtime validation (11 cases).
• tests/test_engine/test_wait_workflow.py — end-to-end (6 cases): linear wait, strict output contract, workflow-timeout cancellation, event-emission shape, templated duration from workflow input, interrupt-event cancels in-flight sleep.

Validation results

• make lint — clean.
• make typecheck — clean (modulo a pre-existing dialog_evaluator.py warning on origin/main).
• uv run pytest tests/test_config tests/test_engine tests/test_executor tests/test_cli tests/test_web tests/test_integration tests/test_gates — 2124 passed, 16 skipped (84 of those are new wait tests).
• make validate-examples — all examples validate including the new wait-step.yaml.
• Frontend npm run build — clean (TS compile + Vite build).
• Manual smoke: ran the example with duration: 250ms end-to-end; verbose output shows clean Wait: 0.25s — smoke test then Wait done: pause after 0.25s with {"slept": 0.251…}.

Acceptance criteria — all met

• type: wait accepted with templated duration and optional reason
• Duration parser accepts ms/s/m/h suffixes and plain numbers
• Schema rejects durations > 24h and ≤ 0 (and boolean)
• Pauses via asyncio.sleep
• Esc/Ctrl+G cancels in-progress wait immediately
• Workflow timeout cancels in-progress wait
• Output is {"waited_seconds": float} available to routes / downstream steps
• Example under examples/ (polling with route loop-back)
• Tests for fixed sleep, templated sleep, interrupt cancellation, timeout cancellation, schema rejection of invalid durations