follow-up: guard-git.sh detect_work_dir sed pattern fails on BSD sed (macOS)

[carlos-alm]

Deferred from PR #1151 review.

Context: While processing PR #1151 from an agent worktree, the push call (using both git -C <path> and cd <path> && style) was incorrectly blocked by guard-git.sh with:

BLOCKED: Branch 'worktree-agent-XXX' does not match required pattern.

The agent ran the command from a parent worktree branch (worktree-agent-XXX), but used git -C / cd to target the PR worktree which was on the valid fix/1136-cargo-rustup-init-shim branch. The hook should have detected the target work dir and validated its branch.

Root cause: detect_work_dir() in .claude/hooks/guard-git.sh uses this sed pattern at line 121:

sed -nE 's/.*-C[[:space:]]+"([^"]+)".*/\1/p;t;s/.*-C[[:space:]]+([^[:space:]]+).*/\1/p'

The ;t; (test-and-branch) syntax is not portable to BSD sed shipped with macOS:

sed: 2: "s/.*-C[[:space:]]+"([^" ...": undefined label ';s/.*-C[[:space:]]+([^[:space:]]+).*/\1/p'

Result: work_dir is empty, the fallback rev-parse --abbrev-ref HEAD runs from the agent's cwd, and the wrong branch is reported.

PR #1146 fixed several BSD sed issues but this ;t; chained pattern was missed.

Fix: Split the two s/.../\1/p patterns into separate -e arguments (or use grep+conditional). The branch was extracted manually inside #1151's flow as a workaround.

Repro:

printf 'gXt -C /tmp push origin foo\n' | \
  sed -nE 's/.*-C[[:space:]]+"([^"]+)".*/\1/p;t;s/.*-C[[:space:]]+([^[:space:]]+).*/\1/p'
# sed: 2: ...: undefined label ...

[carlos-alm]

Already fixed by PR #1146 (commit 1ff4b54, merged 2026-05-17, the day before this issue was filed).

The fix described here — split the s/quoted/.../p;t;s/unquoted/.../p chain into separate sed invocations — is exactly what #1146 did. The current code in .claude/hooks/guard-git.sh (detect_work_dir):

work_dir=$(echo "$search_str" | sed -nE 's/.*-C[[:space:]]+"([^"]+)".*/\1/p')
if [ -z "$work_dir" ]; then
  work_dir=$(echo "$search_str" | sed -nE 's/.*-C[[:space:]]+([^[:space:]]+).*/\1/p')
fi

Verified on macOS BSD sed:

• Old ;t; pattern from the repro → sed: 2: ...: undefined label (broken, as reported)
• Current split-into-two pattern → correctly extracts /tmp from gXt -C /tmp push origin foo

The issue likely referenced pre-#1146 line numbers, missing that the fix had already landed.