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docs/pre2-baseline.md

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+# repo-pre-2 Maintenance Baseline
+
+## Snapshot Identity
+
+`repo-pre-2` was created from the tracked `repo-pre-1` tree without copying
+working-tree-only files or build artifacts.
+
+```text
+planning baseline commit:  ed47f1b5583a229e372f488b9492d1f6234aae98
+snapshot creation parent:  109fe74d3fcef107db5869be1d030f4f12d1cfa6
+snapshot creation commit:  73fa57924b549387400eeeb85354bbbbe770a962
+repo-pre-1 source tree:    6a5a1a49d4a4e08f6ef1155de240500e63a15365
+repo-pre-2 snapshot tree:  6a5a1a49d4a4e08f6ef1155de240500e63a15365
+Linux comparison tree:    b79b9a8b62f633e887a8b99075ff9412fabd7f83
+```
+
+The matching source and snapshot tree IDs establish byte-for-byte content,
+file-mode, and path equivalence at snapshot creation. `repo-pre-1` and
+`src-linux` are read-only references for pre2 work.
+
+## Phase Scope
+
+Pre2 phase 1 is L0 mechanical maintenance alignment. It permits only the
+separately reviewed changes listed below:
+
+1. Remove stale Linux-only declaration fragments from `src/xattr.h` while
+   preserving every active FreeBSD interface.
+2. Remove six specified, unreferenced private constants from
+   `src/erofs_defs.h`.
+3. Rename the private checksum helper in `src/super.c` without changing its
+   signature, body, call position, or behavior.
+
+Each source change must remain an independent commit. This phase does not add
+features, fix behavior, move responsibilities between files, reorder data
+structures, alter ABI, or broadly reformat code.
+
+## Required FreeBSD Differences
+
+Linux and FreeBSD EROFS remain independent implementations. The following
+platform boundaries are intentional and must not be replaced merely to make
+the source look more similar:
+
+- FreeBSD VFS, vnode, mount, namecache, pager, and NFS export interfaces.
+- FreeBSD buffer/cache, GEOM provider, device I/O, locking, and allocation
+  APIs.
+- FreeBSD xattr, ACL, errno, kernel-module, and `bsd.kmod.mk` conventions.
+- FreeBSD build gates, including the current amd64 restriction and optional
+  `ZSTDIO` integration.
+
+Linux naming and layout should be followed only when doing so preserves these
+native contracts and makes cross-repository review easier.
+
+## Excluded Work
+
+This phase does not address vnode ownership after `insmntque()` failure,
+large-run allocation and `uiomove()` limits, compact pblk validation, 48-bit
+boundaries, decompressor descriptors, backend ABI, typed errno, xattr parsing,
+ACL behavior, file splitting, build-system alignment, CI, or test tooling.
+
+## Validation Status
+
+Only static snapshot and Git allowlist checks were performed for the
+initialization commits. No build, QEMU run, test script, smoke test, mount, or
+runtime feature check was performed. All runtime capabilities therefore remain
+`NOT RUN` for repo-pre-2 until a later, explicitly authorized validation phase.