v0.51.550 — Release TI (Transparent Stream activity survives settle/reload)

Release v0.51.550 — Release TI (Transparent Stream keeps its activity after settle/reload)

Ships #4587 (nesquena-hermes) — high-priority activity-stream fix (#4568). Independently agent-reviewed; deep-gated here to the full activity-render mandatory standard (checkpoint matrix + Codex + Opus + suite), with one filter-consistency fix applied during review.

Fixed

• Transparent Stream no longer loses tool calls + thinking when a turn settles or reloads (#4568). The persisted activity scene now renders as transparent event rows on settle/reload (same persisted activity_scene_v1 both modes consume), with intermediate progress prose preserved and only the final-answer-duplicate prose suppressed. Compact Worklog unchanged. Thanks @nesquena-hermes (building on @franksong2702's anchor-scene work).

Gate (full activity-render mandatory standard)

• Checkpoint matrix 4/4 CLEAN (the authoritative gate for this surface): master/transparent reproduces the bug (tools→0); fix/transparent PASS at all 7 checkpoints (during_stream, after_done, switch_away_back, tab_hidden_visible, blur_focus, reload_after_done, reload_mid_stream — 12 tools + 3 thinks + 4 prose interleaved); master/compact + fix/compact PASS (no regression).
• Full pytest suite: 9913 passed, 0 failed
• Codex: SAFE TO SHIP (re-confirm after fix); Opus: SAFE
• Filter-consistency fix applied: aligned the scene-builder/hydrator final-answer filters (messages.js + routes.py) to the renderer's >=80 && ratio>=0.9 rule so a short intermediate-prose prefix of the final answer is preserved (was droppable by the looser builder rule). Re-ran the matrix after the fix → still GREEN 4/4.

Self-contained (does not require #4576 to be merged first — all helpers defined). Closes #4568.