[Improve] Add bounded task-history pagination

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Add bounded, backward get_messages pagination with target- and order-bound continuation cursors.
• Return explicit hasMore, nextCursor, coverage, truncated, and newer-arrival metadata for task and Session history.
• Freeze each read to a commit-time snapshot, preserve deterministic ordering across equal timestamps and resumed/replayed events, and cap transcript payloads.
• Thread cursors through the MCP schema, API member tools, worker client, and readable task-tool output.
• Document the bounded history workflow and add real-database coverage for ordering, concurrency, authorization, and payload limits.

Why this change was made

Visual-proof audits need to reconstruct task stages across older history without requesting an oversized transcript. The previous latest-history behavior could truncate the evidence needed to connect capture entry, review handoff, and delivery.

Impact

Task and Session inspection now defaults to bounded pages and can walk older history until coverage.complete is true. Cursor contents contain only non-secret identifiers and timestamps, while existing task, Session, custom-automation, and Fast-session access checks remain in force. Large message content is explicitly marked as truncated instead of silently inflating the inspection payload.

[roomote-community]

1 issue outstanding. See task

• Fast-session continuation cursors are unstable after a replay updates an existing event's timestamp or turn sequence (apps/api/src/handlers/tasks/fastSessionCommunication.ts:115).

_{Reviewed 5d9be65}

[roomote-community]

The creation-time cutoff does not freeze Fast-session pages. upsertMessage updates an existing event's ts and turnSeq on replay while leaving createdAt unchanged, so a replay after page one can move a pre-snapshot row across this cursor boundary. It still passes this predicate and hasNewer remains false, which can skip or duplicate it on the continuation page. The paging snapshot needs to account for mutable replayed rows (or the stored page ordering needs to be immutable).