Port from openclaw/openclaw#129924: a capture whose pixels are
byte-identical to the previous capture of the same target in the same
session returns its full text metadata (element index included) plus an
explicit 'screen unchanged' note instead of the multimodal image block.
Adapted for Hermes: openclaw gates dedup on per-frame context-epoch
tracking; Hermes bounds staleness with a consecutive-omission streak cap
(2) so full pixels are re-delivered before compaction could evict the
referenced image. Dedup state is per-session (no cross-session leaks),
append-only (no history rewrites — prompt cache prefixes untouched),
and skipped entirely when no session_id is present.
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