Share with a friend shows raw "MCP error -32602: Tool grant_bot_to_friend not found" instead of the unavailable message #563

Symptom (self-test, latest main 4f6a53d798f0)

Two isolated homes (@selftesta2.home / @selftestb2.home), mutual friends with live grants. After one side revokes its Bot grant, Sharing → Share with a friend fails with the raw MCP error:

flybot/social/share-with-friend: MCP error -32602: Tool grant_bot_to_friend not found

Expected

The handler already intends older Bot Social servers to degrade cleanly: grantBotToFriend should return { unavailable: true } and the UI should say "Bot Social needs an update to share with a friend. Invite links still work." (the #500/#516 contract). The REST fallback (POST /v1/bots/:id/grants/to-friend) should be attempted first; when it also 404s, the unavailable path should win.

Actual

The MCP tool-not-found error is not classified as unknown-tool, so no fallback runs and the raw MCP string is shown. isUnknownTool() matches unknown tool, no tool, method not found, unrecognized tool — but the server says MCP error -32602: Tool <name> not found, which matches none.

Evidence from this round:

• production tools/list has no grant_bot_to_friend (it has list_bot_grants / revoke_bot_grant);
• direct REST POST /v1/bots/bot_…/grants/to-friend returns 404 Route … not found;
• isUnknownTool(new Error("MCP error -32602: Tool grant_bot_to_friend not found")) → false.

Steps to reproduce

1. Start two isolated homes on latest main; make them friends so both have a grant (invite A→B, then B→A).
2. Revoke A's Bot grant to B (social/revoke-grant), so B appears in A's share list again.
3. social/share-friends { botId } → B is listed.
4. social/share-with-friend { botId, home: "@selftestb2.home" } → raw MCP error above.

Scope / suggested fix

• plugins/social/src/mcp-client.js: isUnknownTool should also treat Tool <name> not found and -32602 (JSON-RPC invalid params used by the production MCP server for a missing tool) as unknown-tool, so tryTool reaches the REST fallback and { unavailable: true }.
• plugins/social/src/social.js: mapShareFriendError can map the same wording to the friendly unavailable message as a belt-and-braces guard.
• Test: the existing Share a Bot with an existing friend without an invite link #500 test for a server without grant_bot_to_friend uses new Error("unknown tool"); add a case with the production wording MCP error -32602: Tool grant_bot_to_friend not found.

Note: the production Bot Social server still lacks the companion capability itself, so the share action cannot succeed until it ships; the FlyBot-side defect is the fallback/error path. No issue opened in the upstream repo.