session logging, build-only mode, park splash, boot logo spinner

- Per-process stderr logging to /data/log2/{session}/ with time-safe
  directory naming (boot-xxx renamed once GPS/NTP sets clock)
- Aggregate session.log with major events (start/stop, transitions)
- 30-day log rotation cleanup on manager startup
- build_only.sh: compile without starting manager, non-blocking error
  display, kills stale processes
- build.py: copies updated spinner binary after successful build
- Onroad park mode: show splash screen when car is on but in park,
  switch to camera view when shifted to drive, honor screen on/off
- Spinner: full-screen boot logo background from /usr/comma/bg.jpg
  with white progress bar overlay
- Boot logo: auto-regenerate when boot_logo.png changes, 140% scale
- launch_openpilot.sh: cd to /data/openpilot for reliable execution
- launch_chffrplus.sh: kill stale text error displays on startup
- spinner shell wrapper: prefer freshly built _spinner over prebuilt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -57,17 +57,25 @@ chown -R comma:comma /data/openpilot
 
 ### Testing Changes
 
-The launch script now self-cleans — it kills other instances of itself, `launch_chffrplus.sh`, and `manager.py` before starting. No need to manually kill first.
+Always use `build_only.sh` to compile, then start the manager separately. Never compile individual targets with scons directly — always use the full build script. Always use full paths with `su - comma` — the login shell drops into `/home/comma` (volatile tmpfs), not `/data/openpilot`.
 
 ```bash
-# Fix ownership (we edit as root, openpilot runs as comma)
+# 1. Fix ownership (we edit as root, openpilot runs as comma)
 chown -R comma:comma /data/openpilot
 
-# Remove prebuilt to force recompilation (it is recreated after each successful build)
-rm -f /data/openpilot/prebuilt
+# 2. Build (kills running manager, removes prebuilt, compiles, exits)
+#    Shows progress spinner on screen. On failure, shows error on screen
+#    and prints to stderr. Does NOT start the manager.
+su - comma -c "bash /data/openpilot/build_only.sh"
 
-# Must use a login shell as comma — sudo -u won't set up the right Python/env (3.11 via pyenv)
+# 3. If build succeeded ($? == 0), start openpilot
 su - comma -c "bash /data/openpilot/launch_openpilot.sh"
+
+# 4. Review the aggregate session log for errors
+cat /data/log2/$(ls -t /data/log2/ | head -1)/session.log
+
+# 5. Check per-process stderr logs if needed
+ls /data/log2/$(ls -t /data/log2/ | head -1)/
 ```
 
 ### Adding New Params
@@ -85,6 +93,38 @@ The params system uses a C++ whitelist. Adding a new param name in `manager.py`
 - OMX encoder object (`omx_encoder.o`) is compiled by the UI build — reference the pre-built `.o` file rather than recompiling (avoids "two environments" scons error)
 - `prebuilt` is recreated after every successful build — always remove it before rebuilding
 
+## Session Logging
+
+Per-process stderr and an aggregate event log are captured in `/data/log2/{session}/`.
+
+### Log Directory
+
+- Created at manager import time with timestamp: `/data/log2/YYYY-MM-DD-HH-MM-SS/`
+- If system clock is invalid (cold boot, no WiFi, RTC stuck at 1970): uses `/data/log2/boot-{monotonic}/`, renamed to real timestamp once GPS/NTP resolves the time
+- Session directories older than 30 days are deleted on manager startup
+
+### Per-Process Logs
+
+- Every `PythonProcess` and `NativeProcess` has stderr redirected to `{name}.log` in the session directory
+- `DaemonProcess` (athenad) redirects both stdout+stderr (existing behavior)
+- Stderr is redirected via `os.dup2` inside the forked child process
+
+### Aggregate Session Log (`session.log`)
+
+A single `session.log` in each session directory records major events:
+
+- Manager start/stop/crash
+- Process starts, deaths (with exit codes), watchdog restarts
+- Onroad/offroad transitions
+
+### Key Files
+
+| File | Role |
+|------|------|
+| `selfdrive/manager/process.py` | Log directory creation, stderr redirection, session_log logger |
+| `selfdrive/manager/manager.py` | Log rotation cleanup, session event logging |
+| `build_only.sh` | Build-only script (no manager start) |
+
 ## Dashcam (dashcamd)
 
 ### Architecture