feat(service): allow overriding discovery polling interval via env

[nahimterrazas]

Motivation

Discovery polling is the dominant passive RPC cost of a running solver: the boot-time config merge hardcodes polling_interval_secs = 5 for onchain_eip7683, i.e. ~3-4 RPC calls every 5s per chain (~60k calls/day/chain), 24/7, regardless of traffic. Because OperatorConfig has no discovery section and the merge re-runs on every boot, this value could not be changed by bootstrap config, admin API, or storage edits — only by rebuilding.

This is needed to run the hosted solvers in a temporary low-RPC-usage mode (Alchemy CU reduction) while keeping them online.

Change

• New optional env var SOLVER_DISCOVERY_POLLING_INTERVAL_SECS, read during the config merge (same pattern as SOLVER_API_PORT / AUTH_PUBLIC_REGISTER_ENABLED).
• Unset → falls back to COMMON_DEFAULTS.polling_interval_secs (5) — behavior is bit-for-bit unchanged.
• Validated to 1..=300 at merge time: the upper bound mirrors MAX_POLLING_INTERVAL_SECS in the onchain_eip7683 discovery schema (out-of-range values would otherwise pass the merge and abort startup at factory validation); 0 is rejected because the implementation treats it as the currently-disabled WebSocket mode.
• One tracing::info! logs the effective interval at boot for operational verification.
• Documented in AGENTS.md, crates/solver-service/AGENTS.md, and .env.example.

Testing

• test_validate_discovery_polling_interval_bounds — pure range validation (0 / 1 / 5 / 300 / 301), no env access.
• test_discovery_polling_interval_env_override — env var propagates into the generated onchain_eip7683 config.
• test_discovery_polling_interval_defaults_to_seed_default_when_unset — unset falls back through COMMON_DEFAULTS and pins the current default at 5.
• test_parse_u64_env_var_* — new helper parity with the existing parse_u16_env_var tests.
• Env-touching tests use #[serial] + EnvVarGuard and only ever set valid values, so concurrently running non-serial tests can never observe an env state that fails the merge.
• Full cargo test -p solver-service: 724 + 5 passed. cargo fmt --all -- --check and cargo clippy --all-features --all-targets -- -D warnings --allow deprecated clean.

Summary by CodeRabbit

• New Features

  • Added an optional setting to control how frequently on-chain discovery runs.
  • The interval defaults to 5 seconds and accepts values from 1 to 300 seconds.
  • Invalid values are rejected with configuration feedback.
  • Changes take effect after restarting the service.

• Documentation

  • Added configuration guidance, including the default value, valid range, startup behavior, and restart requirement.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e506aefd-80f7-458a-a993-40a70e60d2ea

📥 Commits

Reviewing files that changed from the base of the PR and between 2ae1829 and 049582f.

📒 Files selected for processing (4)

• .env.example
• AGENTS.md
• crates/solver-service/AGENTS.md
• crates/solver-service/src/config_merge.rs

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The solver service now reads SOLVER_DISCOVERY_POLLING_INTERVAL_SECS, validates values from 1 through 300 seconds, defaults to the common seed value, and applies the resolved interval to on-chain discovery. Tests and environment documentation cover the configuration.

Changes

Discovery polling interval

Layer / File(s)	Summary
Parse, validate, and apply polling interval crates/solver-service/src/config_merge.rs	The configuration loader parses and validates the polling interval, logs the resolved value, and replaces the fixed five-second discovery interval.
Validate defaults and document configuration crates/solver-service/src/config_merge.rs, AGENTS.md, crates/solver-service/AGENTS.md, .env.example	Tests cover parsing, bounds, overrides, and defaults. Documentation describes the variable, valid range, default, and restart requirement.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 04958

The change adds a bounded environment override for discovery polling while preserving the existing default behavior. No actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: shahnami, pepebndc, tirumerla

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary change: an environment variable override for the discovery polling interval.
Description check	✅ Passed	The description clearly explains the motivation, implementation, validation, documentation, and tests, but it does not use the template headings or include a related-issue reference.
Docstring Coverage	✅ Passed	Docstring coverage is 81.25% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 1 files. (3 skipped: 3 unsupported.)
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch discovery-polling-env-override

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[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/solver-service/src/config_merge.rs	94.1%	5 Missing ⚠️

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