phase 5.5: polish COLLISION-DETECTION-STATUS for Phases 5.1+5.4

Updates the doc to reflect the 2 follow-on improvements to
collision detection:

- Phase 5.1 added 'recipe files' source (handles the 39 recipes
  with [[package]].files dict). Out-of-scope #1 in this doc
  marked as DONE.

- Phase 5.4 added --selftest mode with 8 regression cases wired
  into the pre-push hook. Future-work item #4 added for property-
  based fuzzing (e.g. hypothesis).

local/docs/COLLISION-DETECTION-STATUS.md

@@ -1,4 +1,4 @@
-# Collision Detection — Status (Updated 2026-07-12, Phase 4.2)
+# Collision Detection — Status (Updated 2026-07-12, Phase 5.5)
 
 ## History
 
@@ -13,15 +13,29 @@
   collision detection at pre-flight time. Located at
   `local/scripts/verify-collision-detection.py`. Wired into
   `local/scripts/build-preflight.sh` with `REDBEAR_SKIP_COLLISION_CHECK=1`
-  bypass env var. **The runtime collision-detection promise in AGENTS.md
-  is now implemented at the build-system level** (rather than in
-  installer source).
+  bypass env var.
+
+- **2026-07-12 (Phase 5.1)**: Extended collision detection to also parse
+  `[[package]].files` (the TOML inline table of install paths used by
+  39 recipes including the Round 3 system drivers like redbear-power,
+  redbear-acmd, evdevd). The forward coverage ensures future recipes
+  using this pattern are caught.
+
+- **2026-07-12 (Phase 5.4)**: Added `--selftest` mode with 8 regression
+  test cases that exercise the algorithm's edge cases (exact match,
+  parent-dir prefix, /etc/init.d override, /etc/environment.d override,
+  non-overlapping, parent-of-subpath, two siblings, different base
+  names). The selftest is wired into `pre-push-checks.sh` so future
+  algorithm changes must keep these cases passing or the pre-push
+  hook fails.
 
 ## How it works
 
 The script compares:
 - **Recipe installs**: `recipes/<cat>/<pkg>/recipe.toml` `[[package]].installs`
-  fields — files the package WILL install at build time
+  fields (canonical list) — files the package WILL install at build time
+- **Recipe files**: `recipes/<cat>/<pkg>/recipe.toml` `[[package]].files`
+  dict (path → source mapping) — also checked (Phase 5.1)
 - **Config [[files]]**: `config/redbear-*.toml` `[[files]]` entries —
   files the config writes before package staging
 
@@ -54,7 +68,8 @@ historical) is not present in the active build.
    `[[package]].files` (different field from `installs`) adds a path
    that conflicts with config, this check doesn't see it. Future work:
    extend `verify-collision-detection.py` to also read
-   `[[package]].files` paths.
+   `[[package]].files` paths. **DONE in Phase 5.1: now reads
+   `[[package]].files` as well as `[[package]].installs`.**
 
 2. **Patch-induced collision** — if a Red Bear patch adds a file to a
    package's install manifest at fork-build time, the pre-flight check
@@ -65,6 +80,12 @@ historical) is not present in the active build.
    creates files at build time that aren't in `recipe.toml`. Those are
    not checked. Future work: trace installer source for generated paths.
 
+4. **In-file test cases** — the `--selftest` mode (Phase 5.4) tests
+   the algorithm against 8 hard-coded cases. A more comprehensive
+   fuzzing test (random paths, deeper prefix trees) would catch more
+   edge cases. Future work: add property-based test using
+   hypothesis or similar.
+
 ## Toggle modes
 
 - Default: report-only (warn if collisions found, build proceeds)