Fixing build & type errors

NO RAW `cargo check`/`tsc` IN THE SHELL WHEN A STRUCTURED PATH EXISTS,
AND NO FIX WITHOUT THE ENCLOSING SYMBOL AND ITS CALLERS IN VIEW.

Announce: "Using tracedecay:fixing-build-and-type-errors."

Choose the entry — this fork matters

Situation	Call	Cost
Compiler output already on hand (pasted or captured)	tracedecay_diagnose (cargo_output, include_callers?) — parses text, maps each error to the smallest containing node with up to 5 callers. Rust/cargo only.	Free — no toolchain run
Need fresh diagnostics	tracedecay_diagnostics (scope: workspace | package+name | file+path) — multi-language (cargo/tsc/pyright), structured, node-mapped.	Heavy — first run on a fresh tree can take minutes (target dir /tmp/tracedecay-target/<project_id>/diagnostics); later runs sub-second

Always prefer the free row. Respect the host's approval/run-mode before running fresh toolchain checks.

Fix loop

1. Map each error class to its cheapest anchoring tool with references/error-class-to-tool.md (undefined symbol → search+signature; arity mismatch → callers; missing field → constructors; trait bound → implementations; etc.).
2. Understand the failing code via the tracedecay:exploring-code ladder; widen with tracedecay_impact when the fix touches a hub.
3. Apply the fix via tracedecay:editing-safely.
4. Re-check with the cheapest applicable path (paste new output into diagnose, or diagnostics with scope: "file"), then verify behavior via tracedecay:assessing-impact.
5. The same error twice after a fix, or 3+ failed fixes → stop patching; re-derive the root cause from callers and types before another attempt.

If tools are deferred or MCP fails

• Deferred: one ToolSearch call — select:tracedecay_diagnose,tracedecay_diagnostics,tracedecay_search,tracedecay_signature,tracedecay_callers.
• MCP error: tracedecay tool diagnose --cargo-output @/tmp/err.txt (the @ reads a file) / tracedecay tool diagnostics --scope file --path … (see tracedecay:using-the-cli). Only if the CLI is also unavailable, run the raw toolchain and paste its output back through diagnose when possible.

Deliverable

Do not end while errors remain unexplained: deliver the grouped diagnostics with enclosing symbols and callers, the applied fix per error class, and a clean re-check (or a precise statement of what still fails and why). Report any tracedecay_metrics: line.