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fix(core): start newly added MCP servers in the background - #53813
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The guarded early plugin activation from #53775 runs the first MCP reconcile before config MCP servers are registered. Servers added on a later reconcile then went through the replace path, which connects them one at a time while the plugin activation batch waits, so providers and integrations did not appear until the slowest server finished starting. Start every server that is new to the reconcile in the background, and keep an explicit MCP.add waiting for its own server to settle.
A server removed or replaced before its background start acquired the per-server lock was still started from its stale entry, leaving an untracked process running until the Location closed.
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Issue for this PR
Regression from #53775.
Type of change
What does this PR do?
Since #53775, a slow MCP server delays startup: models and
/connectstay empty until every configured MCP server has connected, and the servers connect one after another instead of in parallel.Cause: the supervisor now activates the guarded plugins (
OpencodePlugin,ConfigPolicyPlugin) first. Both registerctx.mcp.transform, so MCP's first reconcile runs before the config MCP plugin has added any servers.Mcponly started servers in the background on that first reconcile (!applied && entries.size === 0). The config servers arrive on a later reconcile and go throughreplaceServer, which awaitsstartServerfor each server in turn. That happens inside the plugin activation batch's notify, so the rest of plugin activation waits for it.Fix: any server that is new to the reconcile now starts in the background. The special first-reconcile branch is removed, so new servers take the same path whether they arrive first or later. Readers still wait on each entry's startup latch. Config changes to existing servers still replace them synchronously, as before.
MCP.add(HTTP API, ACP session MCPs) now waits for its own server's startup latch, so it still returns once that server has settled.A background start now checks that its entry is still current once it holds the per-server lock. Without that check, a server removed or replaced before its start ran was still spawned from the stale entry and kept running, untracked, until the Location closed. The first-reconcile path on
v2used the same fork pattern without this check.Remote endpoint startup is still serialized per URL (
endpointLoads), because that lock lives insidestartServer.How did you verify your code works?
servein a clean HOME with two stdio MCP servers that each take 5s to start, pollingmodel.list,integration.listand/api/mcp:b8d3c92985): models at ~2.1s, both MCPs connected at ~7sv2: first response at ~12.2s, MCPs connected one after anotherdoes not wait for MCP servers added after the first reconcile to start: fails on currentv2(the transform hangs) and passes heredoes not start an MCP server removed before its background start: fails without the stale-entry check, passes with itmanages live MCP servers entirely through scoped transforms, which asserted that a newly added server was already connected when its transform returned (the blocking behavior); it now waits for the server to settlebun test test/mcp.test.ts(80 pass); MCP, plugin andtest/plugin/suites (435 pass);bun run typecheckinpackages/coreScreenshots / recordings
N/A
Checklist
Requested by: @neriousy (Filip via Slack)