ElyTree: an unborn HEAD is told from a broken one (G-03, in review)

born() takes a HEAD as new only when it names a branch under
refs/heads/ that no ref holds yet; a broken ref, a tag target or any
other state is an error in Git's words. The branch name keeps every
byte. Round 3 is fixed; round 4 waits until 0.1.3 ships.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tasks/reviews/G-03-r1.md

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+FAIL
+
+- apps/ely-tree/src/git.rs:80 — The HEAD check also treats corrupt references as an empty repository, swallowing real Git errors (rule 2). Reproduction: create a repository with one commit, then replace its current `.git/refs/heads/<branch>` file with `not-an-object-id\n`. On both native Windows and WSL Linux, `rev-parse --verify -q HEAD` exits 1 without output; `born()` returns `Ok(false)`, and both `recover::reflog()` and `structure::lfs()` return `Ok([])`, although `git reflog show HEAD --` reports `fatal: bad revision 'HEAD'`. Recognize only a valid unborn symbolic HEAD as empty; propagate corrupt/unreadable-reference errors and add a regression for this case. Evidence: `.work/G-03-r1/windows-probe.log`, `.work/G-03-r1/linux-probe.log`.

tasks/reviews/G-03-r2.md

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+FAIL
+
+- apps/ely-tree/src/git.rs:86 — `born()` accepts an absent symbolic reference outside `refs/heads/` as an unborn branch, still hiding real Git errors (rule 2). Reproduction on native Windows and WSL Linux: initialize a repository, then run `git symbolic-ref HEAD refs/tags/missing`. `rev-parse --verify -q HEAD` exits 1, `symbolic-ref -q HEAD` succeeds, and `for-each-ref` finds nothing; `born()` returns `Ok(false)` and both reflog and LFS return `Ok([])`, although `git reflog show HEAD --` fails with `fatal: bad revision 'HEAD'`. Require the resolved symbolic target to be a branch under `refs/heads/` before accepting it as unborn; otherwise surface Git's diagnostic, and add a regression for this case. Evidence: `.work/G-03-r2/windows-probe.log`, `.work/G-03-r2/linux-probe.log`.

tasks/reviews/G-03-r3.md

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+FAIL
+
+- apps/ely-tree/src/git.rs:84 — `.trim()` changes valid branch names before checking whether their refs exist, so a valid unborn HEAD still produces repository-page errors (TREE-01, TREE-12, TREE-13). Reproduced on native Windows and WSL Linux: in a committed repository, create branch `topic`, then run `git checkout --orphan` with the name `topic` followed by U+00A0 (non-breaking space). Git accepts the name; `for-each-ref` for its exact `refs/heads/topic<U+00A0>` target succeeds silently with no results. `born()` instead queries the existing `refs/heads/topic` and returns an error, causing both reflog and LFS to return errors instead of empty lists. Remove only Git's output line terminator, preserve the ref name, and add a regression covering this valid unborn branch. Evidence: `.work/G-03-r3/windows-probe.log`, `.work/G-03-r3/linux-probe.log`.