Function is_hidden_reinjection_text 

pub(crate) fn is_hidden_reinjection_text(text: &str) -> bool

True for a <system-reminder>...Your memory was reinjected because your working context was just reset... message — a hidden memory-reinjection turn (frontend/app/view/agent/memory-reinjection.ts’s composeReinjectionMessage). Mirrors that module’s isMemoryReinjectionMessage exactly, including the exact signature string — kept as a literal duplicate rather than a shared constant (Rust and TypeScript can’t share one across the language boundary without extra plumbing this one string doesn’t justify), so a future change to the frontend’s wording must update this function too.

reagentx P0, PR #3502, FOURTH review round: extract_digest_text is the single choke point BOTH next_prompt_suggestion and activity_watcher.rs’s independent 20s periodic sweep funnel through — fixing it here closes the leak for every current and future caller at once, the same “one choke point, not scattered per-consumer patches” lesson hiding-stream-flush-queue.ts already applied on the frontend side, now applied at the layer that actually needed it. Every prior fix on this PR (useAgentActivitySummary.ts’s hidden check, useNextPromptSuggestion.ts’s lastTurnWasHidden) was frontend-only and could only ever gate the frontend’s OWN two RPC call sites — neither could reach activity_watcher.rs’s backend-only sweep, which has no concept of “hidden” anywhere and fires independent of any turn boundary whenever the output FileStore’s size changes. The signature sentence is reason-independent by design — fresh_session triggers (a persistent identity whose prior session could not be resumed; SPEC_HIDDEN_MEMORY_REINJECTION_AFTER_COMPACTION_2026_09_22.md §3.3a) use the same leading sentence as a real compaction, only the second sentence differs (memory-reinjection.ts’s REASON_CLAUSE) — so this one match suppresses both without needing to track which reason fired.