fix(reasonix): stop dropping the [[plugins]] concurrency and auto_start keys

[dyoshikawa]

Problem

Reasonix's [[plugins]] entries accept two scheduling keys that rulesync's REASONIX_PLUGIN_FIELDS allowlist does not carry:

• concurrency — "parallel" or "serial". serial stops two calls to the same server from running at once across the whole session, which is what keeps sub-agents sharing one stdio process from interleaving on its state. With no explicit value Reasonix substring-matches the server name against a known-stateful list (browser, playwright, puppeteer, chrome, chromium, selenium) and serializes a match; an explicit value always wins.
• auto_start (*bool) — false switches the server off: Config.EnabledPlugins drops it from the enabled set, so its tools never reach the model and Reasonix reports it as disabled rather than deferred. Only a durable override in mcp-activation.json outranks the file value.

Because fromRulesyncMcp rewrites the whole plugins key through applySharedConfigPatch, this is not merely "cannot be authored from .rulesync/mcp.json": a value written by hand into reasonix.toml is deleted on the next generate, silently. For these two keys that deletion changes behavior: dropping the key does not fall back to a neutral default, it hands the decision back to the server's name. A serial dropped from a stateful server the name list does not catch puts it on the parallel path; a parallel dropped from a server the list does catch forces it serial; and a dropped auto_start = false switches a deliberately disabled server back on.

Change

Both keys join REASONIX_PLUGIN_FIELDS as passthrough fields, exactly like the sibling timeout keys. The write path and the import path both iterate that list, so authoring, import and round-trip all follow from the one addition. Neither key has a canonical counterpart, so no deep mapping is introduced.

Tests cover export, import, and a round trip. Each pins a value that actually overrides what Reasonix would infer on its own — parallel on a server named browser, serial on one the stateful-name list does not catch, and auto_start: false, the value a truthiness filter would drop.

docs/reference/file-formats.md gains both keys in the Reasonix MCP note.

Verification

Confirmed against the upstream primary source rather than the docs prose: internal/config/plugin_entry.go at v1.38.3 declares Concurrency string \toml:"concurrency"`andAutoStart *bool `toml:"auto_start"`. docs/SPEC.md§3.16 documents the concurrency semantics and the stateful-name default;docs/PLUGIN_PACKAGES.mddocumentsauto_start=falsefor imported servers, andinternal/config/config.go (ShouldAutoStart/EnabledPlugins) plus internal/cli/mcp_manager.go(thedisabledvsdeferredstatus split) are what settle thatauto_start = false` disables rather than defers.

concurrency has no canonical counterpart. auto_start overlaps canonical disabled, but it is left as a passthrough here rather than deep-mapped: Reasonix's activation store can flip a server independently of the file, so the two are not interchangeable, and deciding which wins when a canonical disabled and a hand-written auto_start disagree — in both the write and the import direction — is a separate call left on #2599.

pnpm cicheck passes (411 test files, 11158 tests).

Scope

Refs #2599 — this closes the two MCP gaps recorded in that issue's re-check comments. The issue stays open for its gap 3 (the hook cwd/env fields), which needs a maintainer decision on whether cwd becomes a shared canonical hook key or a Reasonix-only passthrough.

🤖 Generated with Claude Code

https://claude.ai/code/session_019yLN6CVqeZ8HCrjRb9o7mK

[dyoshikawa]

Merged. Thanks — this ships the two [[plugins]] scheduling keys as passthrough fields, so a hand-written concurrency or auto_start survives the next generate.

Two follow-ups stay on #2599: the hook cwd gap, and whether canonical disabled should deep-map onto auto_start (which needs a precedence rule against a hand-written value, in both the write and the import direction).