fix(web): don't re-run the bundled fallback sweep when web-parallel is explicitly disabled

[AIalliAI]

Follow-up to #44433, implementing the non-blocking nit from review (#44433 (comment)) that merged before it could be addressed.

Problem

_ensure_web_plugins_loaded uses get_provider("parallel") is None as the failed-sweep sentinel. With plugins.disabled: [web-parallel] that lookup stays None by design — so the full direct-registration fallback (bundled-dir walk, module imports, provider re-instantiation) re-ran on every web_search/web_extract call even when discovery was perfectly healthy, and each pass overwrote other providers' live registry entries with fresh bundled instances (clobbering e.g. a same-name user plugin or per-instance HTTP session state).

Fix

Treat an explicit web-parallel disable as intentional absence, not a failed sweep — with one carve-out: an empty registry still always triggers the sweep. A failed sweep registers nothing at all (anything escaping _discover_and_load_inner comes from the scan phase, before any plugin registered), so emptiness remains the reliable failure signal that keeps the other bundled backends recoverable even when parallel is disabled.

Also touches up the stale plugins/web/parallel/plugin.yaml description ("Requires PARALLEL_API_KEY") — the backend works keyless via the free hosted Search MCP, which is the premise of #44433's keyless-default guarantee.

Tests

• test_no_resweep_when_parallel_explicitly_disabled — healthy discovery + explicit disable: the fallback never runs across repeated calls, and live registry entries are not replaced (asserts identity). Fails on current main, passes with the fix.
• test_empty_registry_still_sweeps_when_parallel_disabled — failed sweep + explicit disable: other bundled backends are still restored, parallel stays off (pins the carve-out).

tests/tools/test_web_keyless_default_fallback.py + tests/tools/test_web_providers.py + tests/hermes_cli/test_plugins.py: 107 passed. Ruff clean.

🤖 Generated with Claude Code

[AIalliAI]

Requesting maintainer review — this is ready to land from my side. Standalone fork CI is pending first-run approval here; the rollup branch in #44061 carrying this session's batch is fully green on upstream CI (all test shards, typecheck, e2e).

[teknium1]

Closing as superseded by #46350, which has now been merged.

#46350 removes the keyless/free Parallel Search MCP fallback entirely and restores the keyed Parallel behavior, so follow-up fixes that depend on the keyless Parallel default are no longer applicable.

[teknium1]

Closing as superseded by #46350, which has now been merged.

#46350 removes the keyless/free Parallel Search MCP fallback entirely and restores the keyed Parallel behavior, so follow-up fixes that depend on the keyless Parallel default are no longer applicable.