fix(core): make web search limits non-fatal and report real errors

[rekram1-node]

Type of change

• Bug fix

What does this PR do?

A websearch call failed with only Unable to search the web for <query>. Firecrawl had returned 450 KB, 424 KB of it one Hacker News thread, and WebSearchMcp.call fails any response over 256 KB. The tool then replaced that error, like every error without an HTTP status, with the generic message.

Limits no longer fail a search. All six providers (Exa, Firecrawl, Parallel, Tavily, TinyFish, and OpenCode Web Search) now read through plugin/websearch/response.ts:

 WebSearchMcp.call / Tavily / OpenCode Web Search
-  filterStatusOk, read body (MCP: over 256 KB → fail; Tavily and OpenCode: no cap)
+  WebSearchResponse.execute
+    read at most 1 MiB, stop downloading past it
+    non-2xx → same HttpClientError, plus the provider's explanation (read for at most 1 s)
+  parse the body (as partial JSON when it was cut off)
+  decode each result on its own, drop the one that was cut
 WebSearch.query
+  cap each result's content at 4,000 characters

The per-result cap keeps one huge page from pushing the other results out of the 50 KiB tool output; 10 results at the cap still fit. Measured across providers, only Firecrawl (up to 424 KB) and some Exa results (up to 8 KB) exceed it. Parallel sends structuredContent after a text copy of the same JSON, so a cut response falls back to the text copy.

Errors say what happened. The web search errors now have messages, and the tool reports Unable to search the web for <query> (<provider>): <reason>. MCP isError results and JSON-RPC errors now fail instead of becoming "No search results found". Results from real providers:

Case	Before	After
Firecrawl response over the cap	Unable to search the web for …	4 complete results
Firecrawl, free tier rate limit	No search results found…	… (firecrawl): You've hit Firecrawl's free MCP rate limit… Fix: Create an API key at https://www.firecrawl.dev/app/api-keys…
Exa, invalid key	No search results found…	… (exa): web_search_exa error (401): Invalid API key
Tavily, invalid key	Web search authentication failed (HTTP 401)	… (tavily): HTTP 401: Unauthorized: missing or invalid API key.
TinyFish, keyless quota used	Web search authentication failed (HTTP 401)	… (tinyfish): HTTP 401: Free daily Search quota used (50/50). Sign up for continued access: https://agent.tinyfish.ai/sign-up…
Timeout	Unable to search the web for …	… (exa): web_search_exa request timed out

Messages never use the HTTP client's own error text, because it includes the request URL and Exa passes its key in the query string. The 429 failover still reads the status and Retry-After from the same HttpClientError.

Web search tool failures no longer attach the underlying error. toSessionError shows an attached error's message in place of the tool's, which is why the generic text only appeared when that message was empty. Permission errors are still attached and unwrap as before.

How did you verify your code works?

• Real sessions: the dev TUI with a private server from this branch (bun dev --standalone) and Claude Sonnet 5 calling websearch, pinned to each provider through project config:

  • Exa returned 8 results, 3 of them capped at 4,000 characters.
  • OpenCode Web Search returned 8 results.
  • TinyFish and Firecrawl, both out of free quota, stored the provider messages shown in the table.

• Service-level runs against all five external providers without keys and with invalid keys, including Firecrawl's 1.1 MB response cut at 1 MiB.

• New tests:

  • every external provider against a response over the cap, with the oversized result in the middle
  • the per-result cap, including a cut at an emoji
  • MCP isError and JSON-RPC errors
  • provider explanations on non-2xx for TinyFish and Tavily
  • OpenCode Web Search with an oversized response and a 503 { _tag, message } body
  • tool messages for a timeout, a connection failure, and disabled search

  The oversized Firecrawl test fails on v2 with firecrawl_search response exceeded 262144 bytes. The existing test that a rejected OpenCode response is closed promptly still passes.

• packages/core: 5461 pass. The 8 failures are the same shell-tool and test-environment tests that fail on v2. sdk's "embedded client exposes plugin-backed web search" also fails identically on v2.

• bun run check, Prettier, and lint:effect-patterns are clean for the changed files.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR