Return compact JSON from MCP tool and resource responses

[yummybomb]

Summary

MCP tool and resource responses were pretty-printed with JSON.stringify(value, null, 2). The indentation adds nothing for models, and agent harnesses truncate MCP results at fixed limits (pi: 20 KB, Claude Code: 25k tokens, Codex: 10k tokens).

On live webmcp list responses, indentation was 20–37% of the tokens. A 9-tool list drops from 24.0 KB to 17.3 KB, which now fits under pi's limit.

Changes

• All model-facing JSON is now compact: jsonResponse (used by most tools), safeJsonResponse in auth-connections, the browser_repl summary, exec_command, and JSON resources. The data itself is unchanged.
• Two tests that assert exact response text now expect compact JSON.
• Generated package.json and tsconfig.json files stay pretty-printed.

Testing

bun test, tsc --noEmit, and prettier --check pass.

---

Note

Low Risk
Serialization-only change with no API or schema changes; risk is limited to clients that depended on pretty-printed whitespace.

Overview
MCP tool results and JSON resources now serialize with compact JSON (no JSON.stringify indentation) so responses stay smaller under agent harness truncation limits; payload shapes are unchanged.

jsonResponse is the standard path (also adopted by exec_command in shell.ts); safeJsonResponse, browser REPL summaries, and resource templates follow the same rule. AGENTS.md documents the convention, and tests assert compact output where response text is pinned.

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Project	Deployment	Actions	Updated
mcp	Ready	Preview	Oct 19, 2026 2:05pm UTC

[rgarcia]

reviewed — mechanical and correct. local run of bun test src/lib/mcp is 941 pass / 0 fail, and grepping null, 2 across src/, fixtures/, docs/ leaves only src/lib/resolvers/typescript.ts:138-139, which pretty-prints generated package.json/tsconfig.json file contents and is correctly untouched.

nice cleanup on shell.ts — it was the last tool hand-rolling the content: [{type:"text"}] envelope, and the output is byte-identical apart from indentation.

Questions

• src/lib/mcp/responses.test.ts — nothing asserts the compact format. every existing test either JSON.parses the text or compares against JSON.stringify(...), so reintroducing null, 2 in jsonResponse would still pass the suite. one assertion would pin the intent, e.g. expect(jsonResponse({ a: 1 }).content[0].text).toBe('{"a":1}'). the two updated expectations in durable-contracts.test.ts are the same shape, so they don't guard formatting either.

Nits

• src/lib/mcp/responses.ts:34 — ?? String(value) is unreachable for everything that matters (JSON.stringify(undefined) returns undefined). predates this PR, could drop while you're here.
• AGENTS.md:82 — now that the "single-line JSON rather than the pretty-printed house helpers" comment in browsers.ts is gone, nothing records compact JSON as the response convention. optional line in AGENTS.md would replace it.