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fix(mcp): report tool failures as typed MCP errors - #42
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This was referenced Oct 9, 2026
kyle-elliott
added this pull request to stack #45
October 9, 2026 23:21
MCP tools returned failure text inside a successful result, so hosts recorded isError: false for failed calls. The CLI recovered failures by parsing that text. Add one typed failure surface: - `ApiFailure` (client): every non-success HTTP answer carries its status, first typed API error code, bounded Retry-After delay, and the unchanged human text. - `ToolError` and `FailureKind` (query): operation, kind, and detail. `from_client` classifies by the typed cause, not by message text. rmcp marks an `Err(ToolError)` result with isError: true. - One rendering for every tool: `<op> failed: <detail>` and a `next: <step>` line. The `<op> unavailable — ...` form is removed. - `query::*` functions and every `#[tool]` return `Result<String, ToolError>`. `query::cli_result` is removed. CLI commands propagate the error, print only the first line, and exit non-zero. - An unknown codebase selector is an invalid argument that names the accepted values. - An applied edit whose summary cannot be rendered stays a success and names the edit id. No deadline, retry, or index_codebase behavior changes. Refs #37
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Part 1 of 3 for #37, plus follow-up #46. Stack: this PR → #43 → #44 → #46.
Problem
MCP tools returned failure text inside a successful result. Hosts recorded
isError: falsefor failed calls. The CLI found failures by parsing that text (query::cli_result).Change
ApiFailure(src/client/failure.rs): each non-success HTTP answer carries its status, its first typed API error code, the boundedRetry-Afterdelay, and the unchanged human text.ToolErrorandFailureKind(src/query/error.rs):Retryable { after },Unavailable,InvalidArgument,IndexPending,IndexFailed,Refused.ToolError::from_clientclassifies by the typed cause, not by the message text.#[tool]and everyquery::*function returnsResult<String, ToolError>. rmcp marksErrresults withisError: true.<op> failed: <detail>, then anext: <step>line. The<op> unavailable — …form is gone.query::cli_resultis removed.InvalidArgument. The message names the accepted values (an immutable codebase ID or a local directory path) and points tolist_codebases.edit_id.There are no deadline, retry, or
index_codebasebehavior changes in this PR.Verification
cargo fmt --check,cargo test --workspace --locked,cargo clippy --workspace --all-targets --locked -- -D warnings,cargo docwith-D warnings, andgit diff --checkpass.GraphLoadingwithRetry-After, 502, 400/404/422, connect errors), the rendering of each kind,isErrorthrough rmcp, and a CLI exit status that is not zero.