[long-run] Add resumable search epochs with explicit exact and adaptive semantics

[chaoz23]

Parent: #215. Depends on #156 and #217. Feeds #66. Related: #112 and #190.

Product outcome

Turn a marathon into compact, restart-safe epochs so a resource stop preserves its best valid frontier and evidence without requiring one ever-growing process heap.

Contract

• End an epoch at its state grant, a predictive soft-owner watermark, checkpoint/finalization reserve, cancellation/deadline, or exhaustive completion.
• Preserve an immutable result and a validated checkpoint before advancing.
• Make memory/time/resource-stopped work resumable when a safe checkpoint can be produced; preserve the prior known-good checkpoint when it cannot.
• Define two named modes:
  • exact: lossless compact/spill and evidence/order-equivalent resume; no silent eviction.
  • adaptive: deterministic lossy sampling with replayable eviction log; never exhaustive.
• Bind epoch identity to source/configuration, seeds, resource policy, retention policy, and ordered event log.
• Geometric window growth requires a successful commit and reopen of the prior epoch.

Acceptance criteria

• Exact split runs match uninterrupted fixed-state findings, order, frontier, and next checkpoint.
• Cancellation and each resource stop retain a valid partial report and either a current or named prior checkpoint.
• Stale source/configuration/policy/event logs fail closed.
• Checkpoint commit/reopen time and reserve are included inside the declared campaign envelope.
• Adaptive mode records every retained/evicted representative and cannot emit completeness or unreachable claims.
• Protected systematic, rare-prefix, delayed-consequence, and long-tail service floors survive adaptive epochs.
• Tests cover stop during expansion, commit, reopen, and ledger update; corruption; stale revision; tiny epochs; exact migration; and deterministic adaptive replay.

Non-goals

• Making adaptive mode the default before a promotion gate.
• Using recent dryness as proof that a lineage has no future value.
• Provider monetary cost accounting.

[chaoz23]

Dependency checkpoint — 2026-08-25

Current main has exact resumable schema-v1 checkpoints and lifecycle accounting, but it does not produce resource-stop checkpoints or epoch/checkpoint/pressure boundaries. Memory/time stops still return no new checkpoint, and there is no epoch identity or adaptive eviction log.

The required predecessors remain checkpoint-v2/#156, completed #216 telemetry, #190 window sizing, and #217 deterministic owner-pressure behavior. Exact mode must be delivered and proven before any separately named adaptive semantics. This issue remains open.