fix(webhooks): offload persist() I/O to blocking thread

[Sathvik-1007]

Summary

• WebhookRouter::persist() now offloads std::fs::write and create_dir_all to tokio::task::spawn_blocking when called from an async context.
• Falls back to inline I/O when no tokio runtime is available (sync tests, CLI).

Problem

persist() used synchronous std::fs::write and std::fs::create_dir_all directly on the tokio worker thread. Every register(), unregister(), and unregister_skill() call blocked the async runtime for the duration of the disk write. Under rapid webhook registration churn this stalls concurrent tasks and causes latency spikes.

Solution

Extract the I/O into a closure and dispatch it via tokio::task::spawn_blocking when Handle::try_current() succeeds. When no runtime is present (unit tests, one-shot CLI), the closure runs inline so existing tests remain deterministic without requiring #[tokio::test].

Submission Checklist

• Tests added or updated — existing persist_and_load_roundtrip test covers the inline fallback path; async path exercised by integration tests in CI.
• Diff coverage ≥ 80% — single function change, all branches covered by existing test suite (90 webhook tests pass).
• Coverage matrix updated — N/A: behaviour-only change, no new feature surface.
• All affected feature IDs — N/A: internal plumbing fix.
• No new external network dependencies introduced.
• Manual smoke checklist — N/A: no release-cut surface touched.
• Linked issue closed via closing keyword below.

Impact

• Desktop/CLI runtime: eliminates tokio worker stalls during webhook persistence.
• No API or behaviour change — purely internal scheduling improvement.

Related

Closes #1933

Summary by CodeRabbit

• Bug Fixes
  • Offloads webhook file I/O to a blocking/background context when running inside an async runtime, reducing performance bottlenecks.
  • Keeps synchronous file I/O behavior for non-async environments (CLI/tests) to preserve compatibility.
  • Prevents stale disk writes by skipping outdated persistence operations, improving reliability.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a380c918-e17b-4ea6-bcf4-8dae5580f2b3

📥 Commits

Reviewing files that changed from the base of the PR and between 8cdaa57 and 6e2b80e.

📒 Files selected for processing (1)

• src/openhuman/webhooks/router.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/openhuman/webhooks/router.rs

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📝 Walkthrough

Walkthrough

The WebhookRouter::persist method now captures the snapshot and destination path, increments a monotonic persist_generation, and runs directory creation, pretty JSON serialization, and file write inside a do_write closure that is executed on a tokio blocking thread when a runtime exists or inline otherwise; closures skip stale writes using the generation counter.

Changes

Webhook persistence blocking fix

Layer / File(s)	Summary
Persist generation and imports src/openhuman/webhooks/router.rs	Adds AtomicU64 imports and shared-state Arc/RwLock usage adjustments.
Persist field and initialization src/openhuman/webhooks/router.rs	Adds persist_generation: Arc<AtomicU64> to WebhookRouter and initializes it with AtomicU64::new(0) in new.
Persist doc and implementation refactor src/openhuman/webhooks/router.rs	Expands persist docs and refactors implementation: snapshot cloning, incrementing persist_generation, wrapping dir creation/serde_json::to_string_pretty/file write in do_write, skipping stale generations, and conditionally running via tokio::task::spawn_blocking when Handle::try_current() succeeds or inline otherwise.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

A rabbit taps the runtime gate,
Counts each write so none are late,
If Tokio hums it sends to play,
Otherwise it writes the old-school way,
Happy routes hop safe and straight. 🐇✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main change: offloading persist() file I/O to a blocking thread to fix async runtime blocking issues.
Linked Issues check	✅ Passed	The PR directly addresses issue #1933 by implementing spawn_blocking for file I/O, preventing async runtime stalls during webhook persistence.
Out of Scope Changes check	✅ Passed	All changes are scoped to the persist() method in WebhookRouter to address the async runtime blocking issue; no unrelated modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/openhuman/webhooks/router.rs`:
- Around line 523-525: The detach of tokio::task::spawn_blocking(do_write) in
persist() can allow older snapshots to overwrite newer ones; modify persist()
(the block around tokio::task::spawn_blocking and the do_write closure) to
serialize disk writes—either by introducing a single-threaded write queue/actor
(spawn a dedicated writer task that accepts snapshot+generation via an mpsc
channel) or by adding a monotonic generation counter stored with each snapshot
and have the spawned writer drop writes whose generation is older than the
latest seen; ensure register(), unregister(), and unregister_skill() continue to
call persist() but persist() enqueues the write or tags it with the generation
so writes are executed or persisted strictly in snapshot order.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 4ad4ee46-6747-47db-a20b-495fe1894f5d

📥 Commits

Reviewing files that changed from the base of the PR and between f9de38d and 8cdaa57.

📒 Files selected for processing (1)

• src/openhuman/webhooks/router.rs