Cover nested .ignore re-inclusion in the fs walker tests

• Status: Todo
• Kind: Chore
• Authors: jp
• Date: 2026-08-19
• Label: domain=tooling
• Label: type=task

The fs tools support a two-level ignore arrangement that nothing tests: a root .ignore excludes a subtree, and a .ignore inside that subtree re-includes it with !**.

The result is that an unscoped walk from the workspace root does not descend into the subtree, while a walk scoped to that subtree (or deeper) sees it in full. That asymmetry is useful — it keeps a large, irrelevant directory out of broad searches without making it unreachable — but it is entirely emergent.

Why it works

WalkBuilder in .config/jp/tools/src/fs/list_files.rs is built with standard_filters(false), .ignore(true), .parents(true). Only .ignore files are consulted; .gitignore and .git/info/exclude are not. On a broad walk the root .ignore prunes before descent, so the nested file is never read. On a scoped walk the nested file is picked up through parents(true) and its negation applies.

Why it needs a test

PR #727 rewrote this code path (walk_spec now "scopes the workspace walk with a path filter rather than re-rooting") and the behaviour survived, but nothing would have caught it if it hadn't. The failure mode is silent: searches quietly stop seeing a directory, and the tool reports success with fewer results.

Suggested test

In .config/jp/tools/src/fs/list_files_tests.rs: build a temp tree with a root .ignore excluding sub/, a sub/.ignore containing !**, and a file at sub/file.rs. Assert an unscoped listing omits it and a listing with prefix sub includes it.

Worth a matching case in grep_files_tests.rs, which delegates to the same walker for directory targets.