fix(mcp): structured unknown-tool errors, successful empty search, and test coverage (#414, #415, #421)

[sparkysolutions10-pixel]

Resolves #414
Resolves #415
Resolves #421

Summary of Changes

This PR addresses three interconnected issues in the MCP server (src/mcp/server.ts, src/mcp/codes.ts, and tests/mcp.test.ts):

1. Empty Search Handling as Success (An empty result is reported as an error #414):

   • When bazaar_search finds no results ([] or { resources: [] }), it now returns a successful MCP response with { count: 0, resources: [] } rather than treating empty results as ERR_NO_RESULTS (isError: true).
   • Genuinely exceptional failures (non-2xx responses, network timeouts, malformed HTML bodies) remain structured errors with ERR_SERVICE_UNREACHABLE.

2. Structured Error for Unknown Tool Names (An unknown tool name throws a raw exception #415):

   • Calling an unknown tool no longer throws a raw protocol-level JavaScript exception.
   • Returns a structured error with code ERR_UNKNOWN_TOOL that lists valid tools (bazaar_search, paid_call).
   • The untrusted tool name is sanitized (control characters stripped) and bounded to 64 characters to prevent uncontrolled input reflection.
   • Wrapped tool handler execution in top-level error boundary to prevent any uncaught runtime throws.

3. Comprehensive Test Suite (Only the error paths of one tool are tested #421):

   • Added complete coverage for ListTools: verifies advertised tools (bazaar_search, paid_call) and asserts that each tool's inputSchema is valid with required properties.
   • Added full coverage for bazaar_search:
     • Query search path (/discovery/search?q=...)
     • Default resources path (/discovery/resources)
     • Empty result path (verifies success with count: 0, resources: [] without isError)
     • Non-2xx upstream error path (ERR_SERVICE_UNREACHABLE)
     • Malformed/non-JSON response path (ERR_SERVICE_UNREACHABLE)
     • Network failure / ENOTFOUND path (ERR_SERVICE_UNREACHABLE)
   • Added coverage for unknown tool error path, sanitization bounds, and runtime error boundary.
   • Added realistic Horizon transaction error simulation resembling production SDK error structures (op_no_trust).
   • All 16 tests passing under Vitest (npm test).
   • Changeset added under .changeset/mcp-error-handling-and-tests.md.

[Miracle656]

Changes requested: one issue per PR, and only issues assigned to you

This is a process requirement, applied to all 23 of your open PRs in this repo. It is not a judgement about the code, which I have not been able to review — and that is the first half of the problem.

The bundling

Across your open PRs, 150 distinct issues are claimed. This one claims several. #483 claims 22, #481 claims 20, #477 claims 20, #474 claims 20.

A PR that closes twenty issues cannot be reviewed. Each of those issues has its own acceptance criteria — typically five — so twenty issues is a hundred separate things to verify in one diff, and if any one of them is wrong the whole PR is blocked while it is fixed. Every batch I published says the issues are deliberately independent so they can be worked in parallel, by different people, without colliding. Bundling them removes exactly that property.

The assignments

135 of the 150 issues claimed are assigned to other contributors — 67 different people.

This PR is an example: it names issues currently assigned to other contributors who are working on them now. Several have open PRs of their own. If this merged as it stands, those people would have done the work and received nothing for it, and I would have no way to tell the two efforts apart.

I am not assuming anything about why. Assignments change, Drips and GitHub can disagree, and a wide-ranging branch picks up issue numbers easily. But the effect on the people holding those assignments is the same regardless of intent, which is why I have to act on it.

What I need

• One issue per PR. The issue number in the title, its acceptance criteria met, and nothing else in the diff.
• Only issues assigned to you, or unassigned ones you have claimed through Drips. If an issue is assigned to someone else, it is theirs.
• Re-open the work that meets both conditions as individual PRs. I will review them in the order they arrive and at the same pace as everyone else's.

Nothing is being closed. These stay open and are yours to re-cut, withdraw or split as you choose.

Two things worth knowing before you re-cut

Some of this has already landed. #488 (SSRF guard for bazaar_search) and #487 (the paid_call host allow-list) cover the same ground as your #449; #486 covers the MCP README. Check current main before rebuilding something that is already there.

main has moved a long way today — #306, #309, #252, #256, #355, #381, #390, #402, #476, #488 and more. Cut from current main, not from where these branches started.

If you believe an issue named here is genuinely yours, say which and I will check the assignment myself — I would rather be corrected than have someone lose work.