fix(rivetkit-core): return None for empty inspector state to avoid frontend CBOR decode error

[NathanFlurry]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[NathanFlurry]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• fix(rivetkit-core): gate startup until runtime is ready #4736 : 2 dependent PRs (#4737 , #4739 )
• fix(rivetkit-sqlite): preserve text with embedded nul bytes #4735
• chore(rivetkit): add child spans for logging #4734
• fix(rivetkit-core): orphan engine process and detect crashes #4733
• fix(rivetkit-core): return None for empty inspector state to avoid frontend CBOR decode error #4732 👈 (View in Graphite)
• fix(rivetkit-core): don't install tokio::signal::ctrl_c() handler inside serve_with_config #4731
• refactor(rivetkit-core): use subtle::ConstantTimeEq for inspector token verify #4730
• fix(rivetkit): drop is_read_only_sql classifier, surface RETURNING rows #4728
• docs: require close-code rejection for websocket auth/policy failures #4727
• fix(rivetkit): inspector reports actual config state + real queue messages #4726
• fix(rivetkit-napi): plumb ctx through serializeState TSF and stop panicking on runtime_state Ref drop #4725
• chore(rivetkit): remove legacy metrics & prometheus auth #4724
• chore(rivetkit): remove legacy metrics #4723
• chore(rivetkit): impl inspector token #4722
• chore: disable auth on serverless #4721
• chore: fix cors for envoys #4720
• chore: fix serverless in rivetkit-core #4719
• chore(rivetkit): impl follow up review #4711
• chore: rivetkit core/napi/typescript follow up review #4702
• chore: fix remaining issues with rivetkit-core #4701
• chore: sqlite v1 to v2 data migration #4692 : 1 other dependent PR (#4640 )
• chore: move rivetkit to task model #4680
• chore: rivetkit to rust #4679
• feat(rivetkit): sqlite vfs v2 #4673
• chore: rename sandbox -> kitchen sink #4671 : 1 other dependent PR (#4672 )
• chore: configure TLS trust roots for rustls clients #4667
• fix(rivetkit): update config to match envoys & remove manager references #4663
• chore(publish): pin docker base image refs #4652
• chore(engine): publish engine bases in ci #4649 : 2 other dependent PRs (#4650 , #4666 )
• chore: lockfile lefthook #4647
• fix(rivetkit): surface native sqlite kv errors to callers #4645
• fix(rivetkit): prevent sleep races during disconnect and db work #4644
• fix(rivetkit): isolate engine envoys and propagate startup failures #4643
• test(rivetkit): remove wasm sqlite-only fixtures and coverage #4642
• chore(sqlite-vfs): remove wasm sqlite packages and workspace wiring #4641
• chore(rivetkit): remove wasm sqlite runtime #4614
• fix(sqlite-native): restore native startup kv preload #4639
• fix(sqlite-native): delete metadata before chunk range #4638
• fix(sqlite-native): keep truncate cache coherent #4637
• fix(sqlite-vfs): use delete range for truncate cleanup #4636
• fix(sqlite-native): restore kv error hook #4635
• perf(sqlite-native): avoid cloning cached read chunks #4634
• perf(sqlite-native): gate kv operation labels #4633
• perf(sqlite-native): reuse read cache for partial writes #4632
• perf(sqlite-native): remove delete file existence probe #4631
• fix(sqlite-native): gate native read cache behind env var #4630
• fix(pegboard): isolate runner config dc lookup failures #4625 : 1 other dependent PR (#4626 )
• docs(pegboard): note runner config upsert split write risk #4624
• fix(pegboard): unpack global runner config keys correctly #4623
• fix(pegboard-gateway): enforce tunnel message state #4622
• fix(pegboard-runner): clear terminal tunnel routes #4621
• fix(pegboard): skip protocol version keys in runner pool backfill #4620
• fix(pegboard): create missing normal runner configs #4619
• fix(epoxy): reuse cached optimistic value #4618
• main

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[claude]

Code Review

Verdict: Approve with minor notes. This is a focused, correct fix. The root cause is clear — ActorContext::state() returns Vec::new() before any state is persisted, and the previous code wrapped that in Some(vec![]), causing the frontend CBOR decoder to fail on zero bytes. Returning None matches the optional<State> declared in the v4.bare protocol schema for both Init and StateResponse.

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What works well

Correctness. The inspector_state_payload helper correctly maps both "state disabled" (!is_state_enabled) and "no state yet" (state.is_empty()) to None. This aligns with the wire schema and eliminates the decode error.

Lock reduction. The previous code called instance.ctx.has_state() and instance.ctx.state() as separate expressions, which reads the connection_config RwLock twice per site. Caching is_state_enabled before passing it to the helper removes one acquisition per message.

Helper extraction. Extracting inspector_state_payload deduplicates the logic between inspector_init_message and inspector_state_response, and the doc comment explains the why (CBOR failure on empty bytes) rather than the what.

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Issues / suggestions

StateUpdated path is unguarded. inspector_push_message_for_signal still passes instance.ctx.state() directly to StateUpdated { state: ... }. The StateUpdated wire type declares state: State (non-optional), so there is no protocol slot for None here. But an actor that calls save_state with an empty delta would still produce empty bytes on this path. This is lower risk since StateUpdated is only fired after an explicit save, but for consistency consider adding an is_empty() guard and skipping the push (or logging a warning) in that case.

No regression test. The fix is deterministic enough to test: an actor that has never called save_state should produce state: None in the Init message. Adding a test in the existing inspector test module (tests/modules/registry.rs) would prevent this from regressing silently.

PR description is empty. The body is an unfilled template. A one-line description of the bug and how to reproduce it would help reviewers and make the git history more useful.

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Summary

The core fix is correct and the refactor is a net improvement. The StateUpdated gap and missing test are worth addressing before merge, but neither is a blocker if the stacked PR context makes a quick fix impractical.