type-c-service: add power swap functionality and testing

[tullom]

Handle USB-PD power role swaps in the Type-C port and add test coverage.

Previously the port never tore down the old role on a swap, so the power policy rejected the new-role connection. Now process_power_role_swap runs on a power_swap_completed event:

• disable the sink path if consuming
• reset psu_state to Idle, and
• notify the power policy of the disconnect.

The next contract event connects the new role.

Tests cover both swap directions (plug + contract -> power_swap_completed -> new contract), asserting the psu_state transitions and the disconnect -> connect power-policy broadcasts.

Assisted-by: GitHub Copilot:claude-opus-4.8

Resolves #831

[Copilot]

Pull request overview

Summary of changes

This PR adds explicit handling for USB-PD power role swaps in the Type-C controller so that the previous power role is torn down before the new-role contract is established. On a power_swap_completed status event, the port now transitions its local PSU tracking back to Idle, disables the sink path when swapping away from a consumer role, and notifies the power policy of a disconnect so it can accept the subsequent connect in the new role. The PR also adds integration-style tests to validate both swap directions and to ensure the power policy observes a disconnect -> connect sequence across the swap. This directly addresses the reported issue where the power policy rejected the new-role connection because the old role was never cleared.

Changes:

• Add process_power_role_swap() to tear down the prior consumer/provider contract on power_swap_completed before the next contract connects.
• Wire role-swap handling into the port status-changed processing pipeline.
• Add integration tests for consumer→provider and provider→consumer swaps, asserting expected PSU state transitions and power-policy broadcasts.

Step-by-step review guide

1. Role swap teardown in the controller

   • process_power_role_swap() is invoked on power_swap_completed and only acts if the port remains connected and the local PSU state indicates an active connected role.
   • Key behavior: when swapping away from consumer, it calls enable_sink_path(..., false) to safely stop consumption; then it resets the local psu_state back to Idle (clearing caps) and emits power_policy_interface::psu::event::EventData::Disconnected(...) so the power policy stops tracking the old role.

2. Event ordering in process_port_status_changed

   • The swap teardown is intentionally processed before any “new contract” handling (sink_ready consumer contract path, and provider contract change detection). This ordering is what allows the subsequent contract event to be accepted as a fresh connect in the new role.

3. Test coverage for both swap directions

   • The new tests model: initial plug + contract → power_swap_completed → new contract, and assert:
     • the intermediate psu_state becomes Idle after swap completion, and
     • the power policy broadcasts *Disconnected followed by *Connected for the new role.
   • Non-obvious detail: the tests are integration-style (they run the Type-C service task + power policy task concurrently), so correct behavior depends on both the controller emitting the right PSU events and the power-policy service interpreting them as intended.

Potential issues

#	Severity	File	Description	Code
1	Medium	type-c-service/tests/power.rs:611-613	The consumer→provider role-swap test doesn’t assert that the sink path was actually disabled during the swap. Because the harness doesn’t verify unused mock expectations, this test can still pass even if process_power_role_swap stops calling enable_sink_path(..., false) (a key behavior described in the PR).	assert_eq!(port0.port.lock().await.state().psu_state, PsuState::Idle);

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
type-c-service/src/controller/power.rs	Adds process_power_role_swap() to tear down the old role and notify power policy on swap completion.
type-c-service/src/controller/mod.rs	Invokes role-swap teardown when power_swap_completed is present in the status event bitfield.
type-c-service/tests/power.rs	Adds integration tests for consumer→provider and provider→consumer swap flows (disconnect → connect, PSU state transitions).

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.