Conformance: 'Suspicious session state transition to SYNCHRONIZED' layer warning fires once per session (never split out of #1580)

[dfattal]

The OpenXR conformance layer warns on every CTS session:

XrEventDataSessionStateChanged: Suspicious session state transition to XR_SESSION_STATE_SYNCHRONIZED when no frame(s) have been submitted and session has not requested an exit.

• Seen on Windows d3d11 (noted in Conformance (composition, sim-display 2D): projection-layer content is drawn displaced (at the top edge) relative to quad layers at the same world position — GradientFormatsLinearVsNonLinear FAILs on every format #1580 as "tracked here until split out"; Conformance (composition, sim-display 2D): projection-layer content is drawn displaced (at the top edge) relative to quad layers at the same world position — GradientFormatsLinearVsNonLinear FAILs on every format #1580 closed 2026-09-21 without splitting it out) and again on Linux -G vulkan on 2026-09-25: 34 times across the composition category, once per session.
• docs/reference/cts-interactive-procedure.md says an unexplained layer warning invalidates a submission, so this needs either a fix or a documented justification before any conformance submission.
• Likely area: the state tracker's session state machine (src/xrt/state_trackers/oxr/) — the runtime moves to SYNCHRONIZED before the app has submitted a frame. Shared across graphics APIs.

Evidence: Linux interactive run artefacts on the dev box (~/worktrees/cts-runs/), harness from #1738. Related: #1523, #1727.

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