Make the event log the source of truth on every run path - #116
Make the event log the source of truth on every run path#116davidkpiano wants to merge 2 commits into
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runAgent resumes from a self-contained log even when a snapshot is passed; the snapshot is a cache verified by agentMeta.logIndex and state hash, and a diverged cache throws AgentSnapshotDivergedError. Resuming a log that already reached a final state settles instead of hanging. Every @agent.usage event is journaled unconditionally; result.usage folds the log via getUsageFromEvents and in-memory totals are gone. runDurableAgent computes verification hashes per entry from a shadow pure fold (O(1), byte-identical to replay), defaults verification on, and strict-replays the journal at resume. Journaled child completions are rebound onto the current fold, fixing resume from journals written by another incarnation; idle no longer rejects unobserved; onEntry receives the live snapshot. Executors get info.callKey, a deterministic per-call idempotency key that survives crash re-execution on both run paths; provideExecutors accepts a callKey minter for other hosts. The Cloudflare example persists a Durable Object SQLite event log instead of snapshots and resumes through runDurableAgent. A resume-from-every- prefix test pins the durable side state as a pure projection of the log.
🦋 Changeset detectedLatest commit: 78a4656 The changes in this PR will be included in the next version bump. This PR includes changesets to release 7 packages
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📝 WalkthroughWalkthroughChangesThe update makes self-contained event logs authoritative for resume. It adds snapshot divergence checks, durable replay verification, unconditional usage journaling, deterministic executor call keys, and a Durable Object SQLite event-log host with replay-based persistence. Event-log execution
Estimated code review effort: 4 (Complex) | ~60 minutes Merge Risk: 🟡 Moderate · up to Existing durable journals may fail to resume, some resumed conversations may lose message history, and the example host has error-handling gaps. These issues should be resolved before merge. Sequence Diagram(s)sequenceDiagram
participant Client
participant EmailDrafter
participant AgentEventLogStore
participant runDurableAgent
Client->>EmailDrafter: submit event
EmailDrafter->>AgentEventLogStore: read journal
EmailDrafter->>runDurableAgent: resume and process turn
runDurableAgent->>AgentEventLogStore: append journal entries
AgentEventLogStore-->>EmailDrafter: updated entries
EmailDrafter-->>Client: broadcast derived snapshot
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✅ Passed checks (4 passed)
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| const cachedSnapshot = effectiveSnapshot; | ||
| const cachedLogIndex = (cachedSnapshot as { agentMeta?: { logIndex?: number } } | undefined) | ||
| ?.agentMeta?.logIndex; | ||
| if (cachedSnapshot === undefined || cachedLogIndex !== resumeEvents.length) { |
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🔴 Equal-length cache overrides event history
A snapshot from another branch bypasses replay when logIndex matches the supplied log length. The run resumes from unrelated state and ignores history.
Prompt for agents
The fast path in src/run-agent.ts trusts a snapshot solely because agentMeta.logIndex equals events.length. Length does not identify a log prefix, so a snapshot from another fork or thread at the same index can override the self-contained event log. Preserve the event log as the source of truth by verifying equal-length snapshots against the replayed tail, or extend the snapshot stamp with enough lineage and state information to prove it caches this exact prefix before skipping replay. Add a test using two divergent logs of equal length and the snapshot from one beside the events from the other.
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Fixed in 78a4656. The fast path now requires the snapshot's lineage id (agentMeta.logId, the log's executionId) to match and its state hash to equal the tail entry's verification.stateHash. Anything else replays the log and hash-checks the cache at its claimed index. Tests: an equal-length snapshot from a divergent lineage throws snapshot-diverged; a coincidentally identical one resumes from the log.
| if (isRetry) { | ||
| return lastKeyBySite.get(siteId); |
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🔴 Concurrent decisions share idempotency keys
Two actors using the same decision site overwrite lastKeyBySite. A retry can reuse another actor's key and receive its cached result.
Prompt for agents
withCallKeys in src/provide-executors.ts keeps retry state in one Map keyed only by siteId. The wrapped executors are shared by every root actor created from the provided machine, so concurrent decisions at the same site can overwrite each other's last key. Associate the key with the specific invoked decision actor or request instance, matching runAgent's per-self WeakMap behavior. This likely requires threading actor identity to the wrapper rather than recovering retries from a global site map. Add a concurrency test with two root actors whose first decision attempts overlap and then retry.
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Fixed in 78a4656. provideExecutors now memoizes the key per invoked actor (keyed on the invoke's abort signal, which every retry attempt shares) instead of per site. Test: two root actors with overlapping first attempts each reuse their own key on retry.
| } from "@statelyai/agent"; | ||
| import { createAiSdkExecutors } from "@statelyai/agent/ai-sdk"; | ||
| import { emailDrafter, emailDrafterSchemas } from "../email-drafter/agent-logic.js"; | ||
| import { createDurableObjectEventLogStore } from "./event-log-store.js"; |
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🔍 Example uses a local import
The Cloudflare example imports createDurableObjectEventLogStore locally. CONTRIBUTING.md requires self-contained examples with no local imports.
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Keeping the sibling file. Sibling imports are the existing convention in the examples (eve-host, flue-host, langchain-host, email-drafter-inspector all do it), and every host example imports its machine from another example directory. The CONTRIBUTING line targets a shared harness, not one file per example.
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Actionable comments posted: 6
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Inline comments:
In `@examples/cloudflare-agent-host/index.ts`:
- Line 131: Update the WebSocket message handling around JSON.parse to catch
malformed payloads before invoking `#enqueue`; send the existing structured error
response and return without scheduling a turn, while preserving normal
processing for valid JSON messages.
- Line 171: Update the POST error handling around `#view`() to avoid calling it
when `#snapshot` is undefined after initial `#ready`() failure. Return an error body
without the view and status 500 in that case; preserve the existing view
response and status 400 when a snapshot exists after a later turn failure.
In `@src/durable.ts`:
- Around line 432-442: Update the resume replay in runDurableAgent around replay
and the verification option so hash-free journals remain compatible: use
non-strict verification when priorEntries are not fully hashed, while continuing
to validate any hashes that are present. Preserve strict verification for fully
hashed journals.
- Around line 408-413: Update the journal initialization flow around initEntry
so that a non-empty priorEntries collection with hasInit false throws before
creating or appending initLogEntry. Preserve normal initialization for empty
journals and existing init entries, ensuring resumed journals cannot gain a
synthetic index-0 entry after prior entries.
In `@src/run-agent.ts`:
- Around line 2926-2932: The usage-event reuse condition in the event delivery
logic must require object identity with journaledUsageEvent rather than matching
AGENT_USAGE_EVENT_TYPE alone. Remove the type-only disjunct while preserving the
existing undefined guard and reuse of journaledUsageEvent.id for the identical
event object; distinct host-sent usage events must continue to append through
the normal path.
- Around line 2517-2520: Update the replay path around replay and
getPersistedSnapshot so the cached top-level messages are copied onto
replayedSnapshot before assigning effectiveSnapshot. Preserve the existing
cached messages used by the cache-at-tail path, ensuring
getAgentMessages(effectiveSnapshot) and getRequests resume behavior remain
consistent.
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📒 Files selected for processing (24)
.changeset/log-is-source-of-truth.mddocs/choosing-a-run-mode.mddocs/event-log.mddocs/hosts.mddocs/observability.mddocs/persistence.mddocs/snippet-globals.tsdocs/steps.mddocs/usage-and-budgets.mdexamples/cloudflare-agent-host/README.mdexamples/cloudflare-agent-host/event-log-store.tsexamples/cloudflare-agent-host/index.tsexamples/cloudflare-agent-host/metadata.jsonexamples/cloudflare-agent-host/test/agent.workers-test.tsexamples/cloudflare-agent-host/test/event-log-store.workers-test.tssrc/agent-usage-event.test.tssrc/durable.test.tssrc/durable.tssrc/effects.tssrc/index.tssrc/provide-executors.tssrc/run-agent.test.tssrc/run-agent.tssrc/text-logic.ts
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Stamp a per-lineage executionId on the @agent.init entry from runAgent too, and read it back via getLogExecutionId. agentMeta.logId and the callKey prefix now use that id, so keys no longer collide across runs. The equal-length cache fast path requires the lineage id to match and the cache's state hash to equal the tail entry's; anything else replays the log. Cached messages carry across to the replayed snapshot. Usage entry-id reuse compares event identity only. provideExecutors memoizes callKey per invoked actor instead of per site, so concurrent decisions at one site keep their own retry keys. runDurableAgent rejects a non-empty journal without an init entry and resumes hash-free or mixed journals by verifying the hashes present. Cloudflare example: malformed WebSocket frames return the structured error without scheduling a turn; a failed first turn returns 500 instead of dereferencing a missing snapshot.
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Closing: #115 removed the event log, replay, and durable runner this PR was built on. The log-as-truth work will be redone against the simplified API. |
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Summary
The event log is the source of truth on every run path; a snapshot is a verified cache over it. This closes the places where a snapshot or in-memory state was still authoritative.
Changes
runAgentresumeeventslog always drives resume, even when asnapshotis passed.agentMeta.logIndexequals the log length, otherwise the log is replayed and a diverged snapshot throwsAgentSnapshotDivergedError(snapshot-diverged).Usage as a projection
@agent.usageevent is journaled, whether or not the machine declares a transition for it. Delivery to the machine stays gated as before.result.usagefolds the log via new root exportgetUsageFromEvents; in-memory totals are gone. Stragglers append after settle and reachonEvent.runDurableAgentreplay.verificationnow defaults totrue; resume replays the journal in strict mode.onEntry(entry, snapshot)receives the live snapshot.Idempotency key
info.callKey(<logId>:<siteId>#<n>), identical across crash re-execution on both run paths.provideExecutors({ callKey })lets other hosts supply a minter.Cloudflare example
runDurableAgent. No snapshot persistence.Behavior changes to note
Tests
pnpm run check,check:dts, cloudflare workers tests,docs:checkall green.Summary by CodeRabbit
New Features
Bug Fixes
Documentation