Client-side 2026-07-28 support: .discover()/.adopt() + Client(mode=); request-metadata green#2950

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maxisbey wants to merge 9 commits into

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s3-client-modern-path

Commits on Jun 22, 2026

Rename SUPPORTED_PROTOCOL_VERSIONS to HANDSHAKE_PROTOCOL_VERSIONS; consolidate header constant
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Thread per-message headers from session to transport via CallOptions/metadata sidecar
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ClientSession: install per-request stamp at connect time; transport becomes pv-agnostic
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Client gains mode= and prior_discover= policy knobs (legacy and version-pin)
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ClientSession.discover() with the error ladder; Client mode='auto'
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modern_on_request driver + Client in-process modern path via DirectDispatcher peer-pair
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Sweep: route report_progress through DispatchContext.progress; bump LATEST_PROTOCOL_VERSION; orphan cleanup
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Add lifecycle:envelope/discover/mode requirement entries and interaction tests
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Conformance client fixture: drive Client(mode='auto') for the modern leg
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