feat: skip memory startup when Codex rate limits are low

[jif-oai]

Why

Memory startup runs in the background after an eligible turn, but it can consume Codex backend quota at exactly the wrong time: when the user is already near a rate-limit boundary. This PR adds a guard so the memory pipeline backs off when the Codex rate-limit snapshot says the remaining budget is too low.

What Changed

• Added memories.min_rate_limit_remaining_percent with a default of 25, clamped to 0..=100, and regenerated core/config.schema.json.
• Added codex-rs/memories/write/src/guard.rs, which fetches Codex backend rate limits before memory startup and skips phase 1 / phase 2 when the Codex limit is reached or either tracked window is above the configured usage ceiling.
• Keeps startup best-effort: non-Codex auth or rate-limit fetch/client failures preserve the existing memory startup behavior.
• Records a codex.memory.startup counter with status=skipped_rate_limit when startup is skipped.
• Added config parsing/clamping coverage and guard unit tests.

Verification

• Added codex-rs/memories/write/src/guard_tests.rs for threshold, primary/secondary window, and reached-limit behavior.
• Added config tests for TOML parsing and clamping.

[jif-oai]

@codex review

[chatgpt-codex-connector]

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Reviewed commit: 2edff1624b

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[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

codex/codex-rs/memories/README.md

Lines 31 to 38 in e8f899f

	The pipeline is triggered when a root session starts, and only if:
	- the session is not ephemeral
	- the memory feature is enabled
	- the session is not a sub-agent session
	- the state DB is available
	It runs asynchronously in the background and executes two phases in order: Phase 1, then Phase 2.

Update memories README startup conditions

Documented startup behavior is now stale: start.rs adds a rate-limit guard that can skip phase 1/2, but the README still states startup depends only on ephemeral/feature/sub-agent/state-DB checks and then runs both phases. This mismatch can mislead operators when memories.min_rate_limit_remaining_percent causes unexpected skips.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".