install: route through pod-hosted TFTP when power=rack

[widgetii]

Summary

Adds --tftp-via=auto|pod|host (default: auto) and wires _install_async to pick the TFTP backend without forking the U-Boot driving logic.

Mode	What happens
pod	Stage U-Boot + kernel + rootfs in the rack pod's PSRAM via RackController.tftp_put; set setenv serverip 192.168.1.1 and let the camera fetch directly over the local LAN. The pod TFTP server is already on the camera's gateway IP — no host TFTP, no NIC IP plumbing, no sudo, no port-69 conflict. Files cleared at the end via tftp_clear.
host	Existing path. temporary_ip adds a NIC IP alias and start_tftp_server binds UDP/69 on the host.
auto	pod when power=rack, host otherwise — preserves the old default for non-rack setups.

--tftp-via pod without DEFIB_POWER_TYPE=rack errors out cleanly.

Implementation note

A small AsyncExitStack swap. Both branches end up exposing the same two locals to the rest of the install code: serverip (used in setenv serverip) and replace_in_tftp(name, data) (the async hook the UBI rootfs path needs to swap files mid-flow). The 200+ lines of U-Boot driving / tftp + sf write / ethaddr-rescue / saveenv stay untouched.

End-to-end verification

$ DEFIB_POWER_TYPE=rack DEFIB_RACK_HOST=10.216.128.69 \
  defib install -c hi3516ev300 \
                --firmware openipc.hi3516ev300-nor-neo.tgz \
                -p rack://10.216.128.69 \
                --power-cycle \
                --nor-size 16

Phase 1: Burning U-Boot to RAM
  Pod-side fastboot in progress…
  U-Boot loaded in 25940ms
Phase 2: Flash via TFTP
  Staging 6535 KB in pod PSRAM via POST /tftp/<name>...
  Pod TFTP ready on 192.168.1.1:69
  Flashing U-Boot → 0x0 (262144 bytes)
    TFTP CRC verified: FA8B2667
    Flash verified:   FA8B2667     U-Boot OK
  Flashing kernel → 0x50000 (2055676 bytes)
    TFTP CRC verified: BF160C6A
    Flash verified:   BF160C6A     kernel OK
  Flashing rootfs → 0x350000 (4374528 bytes)
    TFTP CRC verified: 7D598D15
    Flash verified:   7D598D15     rootfs OK
  ethaddr preserved
  Environment saved
  Resetting device...
Install complete!

Camera then reaches openipc-hi3516ev300 login: on its own. CRC verification at both the TFTP-into-RAM and flash-readback points, on every partition.

The CLI now drives a complete OpenIPC install from one command, zero host-side TFTP setup — the only network plane involved is the rack-pod's own (HTTP for staging + local-LAN TFTP between pod and camera).

Test plan

• uv run pytest tests/ -x -v --ignore=tests/fuzz — 486 passed / 2 skipped (unchanged — _install_async has no direct unit tests; covered by integration)
• uv run ruff check src/defib/cli/app.py — clean
• uv run mypy src/defib/cli/app.py --ignore-missing-imports — clean
• Regression: defib install --tftp-via host … still works on the existing host-TFTP setups (unchanged code path). Verified by inspection — the host branch is byte-identical to what it was before this PR; the only change is being inside an AsyncExitStack.
• --tftp-via pod without rack power → clean error message.

🤖 Generated with Claude Code