[sunnysab]

Summary

Fix sustained CPU usage after a local configuration change when sync is disabled, paused, or cannot be initialized. No dependency upgrades or polling delays are needed.

Root cause

Sync::touch() records a dirty deadline (now + SETTLE). The background scheduler takes the earlier of this deadline and the next periodic poll.

Sync::round() previously cleared dirty only after ensure() and the paused check. Its early returns for Off, Misconfigured, and Paused therefore left the dirty deadline behind. Once that deadline expired, every subsequent scheduler iteration called sleep_until() on the same past instant. Scheduling the next periodic poll did not help, because the expired dirty deadline continued to win.

Move the existing deadline consumption immediately after acquiring the round mutex, before these early returns. A touch() during the asynchronous engine round still schedules a subsequent round, and the existing periodic polling/retry policy is unchanged.

Reproduction and verification

Reproduced with the shipped 0.81.0 Linux binary using only synthetic configuration and a private temporary directory:

1. Start core with a synthetic control/gateway key, loopback binding, no providers, automatic pricing updates disabled, and no sync section.
2. Let startup finish: CPU usage is approximately 0%.
3. Edit the configuration to rename a client, causing a real configuration reload.
4. Wait past the 10-second settle deadline.
5. Core consumes approximately 113.2% CPU despite /sync reporting off. No desktop client or gateway traffic is required.

The new dirty-deadline regression assertion also fails on unmodified main. With this fix, the same real-process reproduction using a locally built core remains at 0% CPU after the edit.

The regression test covers Off, Paused, and Misconfigured early returns, including a second local change in each state.

Validation

• cargo build --locked -p twcore
• cargo fmt --all -- --check
• cargo clippy --locked --workspace --all-targets -- -D warnings
• cargo test --locked --workspace — 4,017 passed, 0 failed, 9 ignored
• bash scripts/smoke.sh — 84 passed, 0 failed
• Isolated real-process CPU reproduction before and after the fix

The build reports an existing future-incompatibility warning in proc-macro-error2 2.0.1; this change does not alter dependencies.

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[sunnysab]

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