security: sanitize Perplexity API error messages (CWE-200; re-impl of #103)

[jliounis]

Summary

Re-implementation of the previously-closed #103. Credit: @sebastiondev for the original analysis and patch.

Vulnerability

CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) — Medium severity.

makeApiRequest, performChatCompletion, and performSearch previously embedded raw upstream details into thrown Error messages:

throw new Error(`Network error while calling Perplexity API: ${error}`);
throw new Error(`Perplexity API error: ${status} ${statusText}\n${errorText}`);
throw new Error(`Failed to parse JSON response from Perplexity API: ${error}`);

The MCP SDK returns thrown tool errors verbatim to remote callers in result.content[].text. Because this server can also run as an unauthenticated HTTP service bound to 0.0.0.0, a remote MCP client can trigger upstream failures and read back:

• the upstream response body (provider internal traces, account hints, etc.)
• raw exception text from the network layer (proxy/DNS details, internal hostnames)
• raw JSON-parse exception text (may include partial payloads)

Fix

Separate operator diagnostics from caller-visible errors:

• The full upstream body, parser exception, and network exception text are now logged server-side via the existing logger (writes to stderr; survives STDIO transport).
• The Error that bubbles up to the MCP SDK now contains only a stable, generic, non-secret message:
  • Perplexity API error: <status> <statusText>
  • Network error while calling Perplexity API
  • Failed to parse JSON response from Perplexity API
  • Failed to parse JSON response from Perplexity Search API
• Timeout and validation errors are unchanged (they were already sanitized).

Tests

• Updated should handle error text parse failures to assert the sanitized output and the absence of the underlying exception text.
• Added 3 new CWE-200 regression tests:
  • JSON parse error must not leak parser exception text
  • Network error must not leak network exception text
  • Upstream 4xx/5xx must not leak the response body or trace
• npm test: 81 passed / 81 (was 78 on main).
• npm run build: clean.

Backward compatibility

• The status + statusText prefix and the four generic strings are preserved exactly as before, so any client that pattern-matches on "Perplexity API error: 401" etc. continues to work.
• The only thing removed is the trailing detail block — which was the leaky part.