feat(session)!: handle Auto-Detect Request PDUs from server

[Greg Lamberson (glamberson)]

Fixes a crash when the server sends Auto-Detect Request PDUs during an
active session. After #1176 added ShareDataPdu::AutoDetectReq routing,
these PDUs decode correctly but hit the catch-all error path in the x224
processor: "unhandled PDU: Auto-Detect Request PDU".

Per [MS-RDPBCGR 2.2.14], the client must respond to RTT Measure
Requests by echoing the sequence number. Without this, servers that
probe RTT (Windows Server, or IronRDP servers using #1177) get no
response, and the session terminates.

Changes:

• Handle RttRequest by auto-responding with RttResponse (echoes the
  sequence number per spec). Follows the ShutdownDenied pattern already
  used in the processor for protocol-mandated auto-responses.

• Surface NetworkCharacteristicsResult as a new
  ActiveStageOutput::AutoDetect(AutoDetectRequest) variant. This
  carries server-computed RTT and bandwidth metrics for applications
  that want adaptive behavior.

• Log and return empty for BW_START/BW_PAYLOAD/BW_STOP until the
  bandwidth measurement state machine is implemented. This prevents
  crashes without incorrect protocol behavior.

• Update all in-tree exhaustive matches: ironrdp-client, ironrdp-web,
  FFI.

• 6 tests in ironrdp-testsuite-core: RTT response generation, sequence
  number preservation, NetworkCharacteristicsResult surfacing, and
  crash-prevention for each BW variant.

Depends on: #1168 (merged), #1176 (merged)
Related: #1177 (server-side RTT), #1158 (multi-codec pipeline)

BREAKING CHANGE: ActiveStageOutput and ProcessorOutput have new
AutoDetect variants. Consumers with exhaustive matches must add an arm.

[Copilot]

Pull request overview

Adds active-session handling for server-sent Auto-Detect Request PDUs (MS-RDPBCGR 2.2.14) in the session layer to prevent crashes and to respond to RTT probes as required by the protocol.

Changes:

• Implement Auto-Detect request handling in x224::Processor, including automatic RTT responses and surfacing NetworkCharacteristicsResult as an output.
• Thread the new AutoDetect output through ActiveStageOutput and update in-tree consumers (client, web, FFI) to handle the new variant.
• Add a new session testsuite module covering RTT response generation and non-crashing behavior for bandwidth PDUs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
crates/ironrdp-session/src/x224/mod.rs	Handles Auto-Detect PDUs on the IO channel (RTT auto-response, surface netchar results, ignore BW PDUs).
crates/ironrdp-session/src/active_stage.rs	Introduces ActiveStageOutput::AutoDetect and maps it from x224::ProcessorOutput.
crates/ironrdp-client/src/rdp.rs	Adds an exhaustive match arm for the new ActiveStageOutput::AutoDetect.
crates/ironrdp-web/src/session.rs	Adds an exhaustive match arm for the new ActiveStageOutput::AutoDetect.
ffi/src/session/mod.rs	Extends FFI output enum typing to include AutoDetect.
crates/ironrdp-testsuite-core/tests/session/mod.rs	Registers the new autodetect test module.
crates/ironrdp-testsuite-core/tests/session/autodetect.rs	Adds tests for RTT auto-response, netchar surfacing, and BW request crash-prevention.

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[Greg Lamberson (glamberson)]

I'm doing lots of nonstandard testing, and this PR addresses some of those test cases for me...

This unblocks server implementations that need to support V8 clients without H.264: xfreerdp in software-only mode, RustConn, and older mstsc builds. Without this method, the only option for non-AVC clients is falling back to FastPath bitmaps, which loses frame acks and QoE tracking.

Thanks.