Native file tools: include the attempted path and operation in filesystem errors #183

Motivation

Native file-tool failures can surface only as error: FileNotFound, omitting the tool, supplied path, and failed operation. This prevents users and agents from distinguishing a missing read/edit target from a missing parent directory during file creation.

Current behavior / evidence

The outer dispatcher formats propagated failures generically:

• src/exec.zig:75-91
• src/tools.zig:352-355

Affected operation sites include:

• read_file: src/exec.zig:204-220
• edit_file: src/exec.zig:276-294
• write_file: src/exec.zig:321-332

Proposed behavior

Map expected filesystem failures at the operation site, where the tool, supplied path, and semantic operation are known.

At minimum:

• read_file reports that its target could not be opened/read;
• edit_file reports that its target could not be opened for editing and suggests write_file if creation was intended;
• write_file identifies a missing parent component rather than implying that a new output file must already exist.

Preserve more-specific confinement, symlink, permission, and validation errors.

Acceptance criteria

• Missing-target errors from read_file and edit_file identify the tool, supplied path, and operation.
• write_file distinguishes a missing parent directory from a valid nonexistent output target.
• The underlying error category remains available.
• Results remain marked is_error = true.
• Existing cwd-confinement and symlink-escape diagnostics retain precedence.
• Existing argument, binary-file, range, and old_string diagnostics are unchanged.
• Diagnostics do not expose unrelated host paths or secrets.
• Regression tests cover a missing read target, missing edit target, missing write parent, and successful new-file creation.

Related issues

• edit_file strips executable bit from existing scripts #179 — executable-bit preservation by edit_file
• Route in-repo file reads through codedb read --compact on the codedb path (token savings) #66 — compact in-repository file reads
• Plan mode blocks legitimate read-only exploration of user-specified sibling repos #64 — external-path policy