fix(statusline): make cost formatting locale-independent

[cdeust]

Summary

On a host with a comma-decimal locale (LC_NUMERIC=fr_FR.UTF-8) the statusline cost ledger reported $0. Two independent defects compound.

1. costs.sh had no locale guard (grep -c LC_NUMERIC costs.sh → 0). Its awk emitted 19,779682 and wrote that comma value into the per-session cache; downstream arithmetic coerced it to 0.

2. The render path interpolated the value into the awk program text, so LC_NUMERIC=C was applied on the wrong side — by then the comma is syntax, not data:

LC_NUMERIC=C awk "BEGIN{printf \"%.2f\",19,779682}"   ->  19.00   # two printf args
LC_ALL=C     awk -v v="19.779682" 'BEGIN{...}'        ->  19.78

Fix

• export LC_ALL=C at the top of costs.sh and statusline-command.sh — every awk/printf emits dot decimals regardless of the user's locale. Only numeric format specifiers (%Y-%m-%d, %02d) are used elsewhere, so date output is unaffected.
• fmt_usd (format.sh) and cost_fmt (render.sh) now pass the value via awk -v and normalise a stray comma, so a malformed value can never become program syntax.

Verification

Measured on a fr_FR.UTF-8 host, before → after:

Check	Before	After
costs.sh today	0	76.543286
costs.sh month	0 0	76.543286 76.543286
fmt_usd 19,779682	$19.00	$19.78
fmt_usd 19.779682	$19.78	$19.78 (unchanged)
fmt_usd 1234.5	$1.2k	$1.2k (unchanged)

bash -n clean on all four files.

Upgrade note

Caches already written with comma decimals must be purged once — they regenerate with dot decimals on the next refresh:

grep -l ',' ~/.claude/statusline-costs.jsonl.* 2>/dev/null | xargs -r rm -f

Regression origin

The previous monolithic statusline-command.sh read .cost.total_cost_usd straight from the payload — a JSON number, locale-independent. The modular refactor introduced the costs.sh ledger layer, which was not locale-safe.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JMNwLEZS6SsrWMLwd1cQ6p