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docs/pre13-h03b.md

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+# Pre13 H03b: qstr block and dirent search
+
+## Scope
+
+- Converted `find_target_dirent()` and `erofs_find_target_block()` to accept a
+  bounded `struct erofs_qstr` search key.
+- Constructed bounded on-disk qstr objects from the same validated dirent name
+  offsets and block end pointers used before this change.
+- Constructed a temporary search qstr inside `erofs_namei()` while retaining
+  its original pointer/length external interface for H03c.
+- Removed the H03a legacy comparator adapter.
+
+No changes were made to `dir.c`, readdir, cookies, buffer ownership, directory
+validation, binary-search decisions, errno selection, cleanup, VOP lookup,
+vnode locking, or namecache operations.
+
+## Static evidence
+
+- `erofs_dirnamecmp()` has exactly two call sites: the block-level first-name
+  comparison and the candidate block's dirent comparison.
+- Both on-disk qstr end pointers use the same next `nameoff` or validated block
+  boundary as the previous pointer arguments.
+- `erofs_find_target_block()` retains every `erofs_brelse()` path, candidate
+  replacement, `EINTEGRITY` assignment, and `ENOENT` distinction.
+- `erofs_namei()` still releases the selected block once and returns `ENOENT`
+  only for a true miss.
+- The `erofs_lookup()` control flow and all `cache_enter()`, `vn_vget_ino()`,
+  `erofs_vget()`, and `cn_lkflags` uses are outside this stage's diff.
+
+## Comparator gate
+
+Tests baseline: `ce03c283e6e2cb8f1b69c8eff21f7d06098a4fbe`.
+
+- Python deterministic corpus: PASS, 11,562 cases.
+- Independent C harness: PASS, 1,048,576 cases.
+
+The comparator gates are host static-equivalence evidence, not dynamic feature
+tests.  H03 still requires TC042, TC043, TC044, TC045, TC053, TC054, TC123,
+TC141, and TC148, followed by the final smoke test.