fix: use stdin session cost, remove JSONL calculation, harden hook bypass

Author: barkain

CHANGELOG.md

@@ -5,9 +5,14 @@ All notable changes to this project will be documented in this file.
 ## [1.15.2] - 2026-04-04
 
 ### Fixed
-- **$0.00 cost display**: Use `cost.total_cost_usd` from stdin JSON for real-time session cost; daily cost already uses JSONL self-calculation (no ccusage dependency)
+- **Session cost from stdin**: Replaced all daily cost self-calculation (JSONL scanning, background refresh, cost cache) with simple `cost.total_cost_usd` read from stdin JSON -- zero I/O, real-time session cost
 - **Delegation hook subagent deadlock**: Expanded subagent bypass to check `CLAUDE_AGENT_ID` and `CLAUDE_SCRATCHPAD_DIR` in addition to `CLAUDE_PARENT_SESSION_ID`; added redundant safety net inside `main()`; normalized `CLAUDE_PROJECT_DIR` path resolution with `Path.resolve()`
 
+### Removed
+- `_find_todays_session_files()`, `_sum_session_cost()`, `_cost_from_usage()`, `fetch_costs_raw()`, `spawn_background_refresh()`, `load_cost_cache()`, `save_cost_cache()`, `is_cache_valid()`, `_is_refresh_locked()` -- all replaced by stdin session cost
+- Cost cache constants (`COST_CACHE_FILE`, `COST_CACHE_TTL_SECONDS`, `COST_REFRESH_LOCK`) and lock file logic
+- `time` import (no longer needed)
+
 ## [1.15.1] - 2026-04-04
 
 ### Fixed