Fix /statusline install bugs on macOS/BSD (v1.5.1)

[gering]

Summary

Three bugs found while migrating a manual ~/.claude/statusline.sh to the plugin-managed version on macOS. All three caused silent failures — the install reported success but the status line broke in different ways. Patch bump 1.5.0 → 1.5.1.

Bug 1 — BSD awk writes empty file

BSD awk (macOS default) rejects newlines inside -v variable values with a newline in string warning and produces empty output. mv then silently overwrites the target with zero bytes. bash -n "" passes (empty script is syntactically valid), so the install's verify step did not catch it.

Fix: prescribe python3 (always available on macOS/Linux) for the marker block mutation. Explicitly forbid awk -v "$multiline_var" in the SKILL.md. Add post-write checks: file non-empty + marker count exactly 1 + BEGIN line < END line, in that order, before bash -n.

Bug 2 — placeholder placed before OUT= initialization

If the user drops # {{cks}} before the line that initializes $OUT, the injected marker block runs against an empty accumulator and the subsequent OUT="..." overwrites the cks contribution. No error — cks just disappears.

Fix: detect via line-number comparison. PLACEHOLDER_LINE must be strictly greater than LAST_OUT_LINE (the line number of the last ^[[:space:]]*OUT= assignment in the file). Abort with a specific error pointing to both line numbers if not.

Bug 3 — symlink target without +x

When ~/.claude/statusline.sh is a symlink managed by stow/chezmoi/etc., the link target may not carry the executable bit. Claude Code execs the command directly via execve, which requires +x on the resolved file. bash ~/.claude/statusline.sh from a test shell works (bash does not need +x), so the bug only surfaces in actual Claude Code sessions — no status line at all, no error.

Fix: resolve the symlink in step 0 (python3 -c "import os,sys; print(os.path.realpath(sys.argv[1]))" "$STATUSLINE" → STATUSLINE_TARGET). In preflight, check [ -x "$STATUSLINE_TARGET" ] and auto-chmod +x if missing (with an explanatory message).

Bonus — symlink-aware atomic mv

All mutations now operate on STATUSLINE_TARGET (resolved real path), so the temp file lives on the same filesystem as the destination → os.replace is truly atomic. Previously, a symlink pointing across filesystems could cause mv to fall back to copy+delete or fail outright.

Implementation notes

• Both install and uninstall now use python3 for in-place edits, never sed -i or awk -v.
• Step 0 of SKILL.md introduces STATUSLINE_TARGET and a tooling-rationale note that future implementers cannot ignore.
• Verify step (2e) is now a four-item ordered checklist: non-empty → marker count/order → bash -n → exec bit retained. Restore from named $BACKUP on each failure.
• Uninstall (5a) mirrors the same Python3 + atomic + verify pattern.

Test plan

• On macOS with default BSD awk: run install against a real ~/.claude/statusline.sh and verify the file is non-empty after mutation
• Place # {{cks}} before the host's OUT="..." line, run install → expect abort with line-number-specific error
• Place # {{cks}} after the last OUT= line, run install → expect successful placement
• Run install against a ~/.claude/statusline.sh symlink whose target lacks +x → expect auto-chmod + explanatory message
• Verify the renderer at ~/.claude/cks-statusline.sh is still copied with +x after the install
• Run uninstall → expect marker block stripped, file still non-empty + executable, bash -n passes
• Run install then uninstall on a symlinked statusline.sh hosted on a separate filesystem (e.g. stow setup) → expect atomic mv works on the resolved target

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