Calibrated acceptance ETA and stage checkpoints (WS-043)

WS-043 estimates the next acceptable outcome for a delivery or stage checkpoint. Forecasts are stored separately from WS-041 measured usage/time observations and are append-only: historical rows are never rewritten.

Surfaces

• Core: awr_core::workstream_eta — critical-path / concurrency schedule, forecast records, calibration gate, reestimate links, sample/acceptance isolation.
• Store (schema 14 / eta_checkpoints): append-only eta_forecasts, isolated eta_sample_ledger and eta_acceptance_data, idempotent ingest receipts.
• Runtime: estimate_and_persist, reestimate_and_persist, query helpers, and observation_handoff_for_estimate (consumes WS-041 handoff without treating cumulative duration as remaining ETA).

Invariants

1. Forecast records capture target, generated_at, task-graph version, execution strategy, sample/method versions, intervals, assumptions, and unknowns. Persistence refuses in-place rewrites.
2. Scheduling uses dependency critical path, real concurrency limit, and available executors. Parallel task durations are never summed into the checkpoint ready time. A card waits only on its dependency closure, not on every mainline.
3. Effective execution, dependency/human wait, and calendar acceptance window are separate components. Network/model queue exclusions require an observable evidence_ref; missing components stay Unknown.
4. Cold start may be Provisional { source } or Unestimable { reason }. Calibrated intervals require the frozen sample + holdout policy gate. Reports coverage (bps), interval width, absolute error, and missing rate. LLM narrative may be recorded as an assumption, never as a precise promise.
5. New dependency, rework, executor change, or capacity change triggers a new forecast that supersedes the prior id with before/after reasons. Historical samples stay isolated from acceptance data.

Fixtures: tests/fixtures/workstreams/eta-checkpoints/.