feat: replace ModemManager with pure Python AT state machine

[juzigu40-ui]

This PR replaces ModemManager AT-command handling with a pure Python AT state machine.

What is implemented

1. Dual-chip support (EG25 + EG916) with one state machine

   • The modem type is detected at startup via ATI.
   • EG25 and EG916 use chip-specific setup commands, but both go through the same core state flow.

2. No D-Bus dependency in the pure modem path + shared-memory state export

   • The Python modem path uses direct serial AT commands only.
   • State transitions are written to /dev/shm/modem_state.txt (e.g. CONNECTING, CONNECTED).

3. WiFi-over-LTE route priority

   • Route metrics are explicitly adjusted so WiFi wins when both links are present.
   • Implemented using Linux route commands in the modem setup path.

4. Fast cold-boot path

   • Non-essential waits were reduced.
   • Minimal attach sequence is used (AT+CGATT=1, AT+CGACT=1,1) to prioritize first connectivity.

Files

• system/hardware/tici/pure_python_modem.py
• system/hardware/tici/hardware.py
• system/qcomgpsd/at_port_interceptor.py
• system/hardware/tici/tests/test_pure_python_modem.py
• tests/test_pure_python_modem.py

Local tests

• pytest -q --noconftest -o addopts='' tests/test_pure_python_modem.py
• Result: 4 passed

Community Validation Runbook (Copy/Paste)

1) No-hardware smoke (simulated state machine)

cd openpilot
python3 system/hardware/tici/pure_python_modem_dry_run.py   --simulate   --simulate-transient-fail   --state-path /tmp/modem_state_dry_run.txt   --json

Expected result:

• result.attached == true
• result.published_state == "CONNECTED"
• AT trace includes a recovery cycle (AT+CFUN=0 -> AT+CFUN=1) before final attach.

2) Real-device run (comma 3X / comma 4)

cd openpilot
sudo OPENPILOT_PURE_MODEM_STRICT=1   OPENPILOT_MODEM_TTY=/dev/ttyUSB2   OPENPILOT_MODEM_APN="<your-apn>"   OPENPILOT_MODEM_REG_TIMEOUT=45   OPENPILOT_MODEM_STARTUP_RETRIES=1   python3 system/hardware/tici/pure_python_modem_dry_run.py --json --enforce-route

Expected result:

• state=ATTACHED, attached=true
• /dev/shm/modem_state.txt transitions to CONNECTED

3) Route priority check (WiFi > LTE)

ip route | grep default

Expected result:

• WiFi default route keeps lower metric than LTE route.

4) Test report template

Device: comma 3X / comma 4
SIM Carrier + APN: <carrier/apn>
Boot to first ping (google.com): <seconds>
Run result: ATTACHED=<true/false>, model=<EG25/EG916>
modem_state.txt final value: <CONNECTED/...>
Route metrics snapshot: <paste ip route default lines>
Any reconnect events observed: <yes/no + short log>

[juzigu40-ui]

Updated this PR with a copy/paste validation runbook:

• no-hardware simulated dry-run (with transient attach failure + recovery)
• real-device execution command for comma 3X/comma 4
• route-priority verification (WiFi > LTE)
• standardized report template for testers

Also pushed a pure_python_modem_dry_run.py diagnostic tool to make validation reproducible from one command.