MCP source loses configured auth on next boot

[aryasaatvik]

Problem

When executor.jsonc declares a remote MCP source with auth.kind: "header" or auth.kind: "oauth2", boot-time replay persists the source row to the DB without the auth field. Every tool call against that source then goes out unauthenticated.

After #364 (5dc4aa8f mcp: allow saving oauth2 source before sign-in), the failure mode got harder to spot: the row still lands in the catalog with auth.kind: "none" (defaulted from undefined input), so the source appears fine in the UI but is silently misauthenticated.

Related but distinct: #229 covers the UI-side flow where users can't supply a header auth at probe time. This issue is the inverse — auth that was successfully configured (file or UI) is lost across the next restart.

Reproduction

1. Add an entry to executor.jsonc:

   {
     "kind": "mcp",
     "transport": "remote",
     "name": "PostHog",
     "endpoint": "https://mcp.posthog.com/mcp",
     "namespace": "posthog",
     "auth": {
       "kind": "header",
       "headerName": "Authorization",
       "secret": "secret-public-ref:posthog-api-key",
       "prefix": "Bearer "
     }
   }

2. Provision the posthog-api-key secret (e.g. via keychain).
3. Restart the local executor.
4. Inspect the row:

   sqlite3 ~/.executor/data.db "SELECT name, config FROM mcp_source WHERE id = 'posthog';"

   config.auth.kind is "none" instead of "header".

Root cause

apps/local/src/server/config-sync.ts:123-132 — the remote-MCP branch of addSourceFromConfig builds the executor.mcp.addSource input without an auth field. Dates to 807df1de chore: fix data storage (#262), where boot-time file→DB replay was introduced and the field was missed.

The MCP plugin's write-back (packages/plugins/mcp/src/sdk/plugin.ts authToConfig) correctly serializes auth into the file when a source is added through the UI, so the file ends up right — but the inverse path on boot drops it. The forward and inverse translators live in different packages, which is why drift went unnoticed.

Fix

Translate the file-shape McpAuthConfig (header secret: "secret-public-ref:<id>") into the runtime McpConnectionAuth (header secretId: "<id>") and forward it.

Worth pairing with a small consolidation:

• Move authToConfig out of the MCP plugin, alongside its new inverse mcpAuthFromConfig, into @executor/config next to the schema and the existing headerToConfigValue helper. The secret-public-ref: prefix stops leaking into plugin code.
• Roundtrip test (toConfig ∘ fromConfig === identity, both ways) for every auth discriminant — adding a new kind without paired updates fails at test time, not at a user's boot.

PR with fix + consolidation incoming.

Acceptance

• A header-auth or oauth2 entry in executor.jsonc survives restart with the same auth shape in the DB.
• Roundtrip transform tests cover every auth discriminant.
• UI add/remove flows unchanged.