Chat transcript navigation product specification

Purpose

Long sessions cannot always keep every message loaded and rendered. Transcript navigation therefore has two distinct responsibilities:

choose which part of session history is loaded;
move the viewport within the loaded messages.

Users should be able to inspect earlier or later history without losing the message they were reading, while still having direct ways to reach the oldest and newest currently loaded content.

Terms

Session history is the ordered message sequence in the selected live session or read-only session snapshot.

Message index is a zero-based position in that session-history snapshot. It is not a stable identity across mutations that insert or delete earlier messages.

Loaded range is the subset of session history currently held by the chat controller.

Viewport is the visible portion of the loaded range.

Visual top and visual bottom are the user-visible transcript edges, independent of whether the native list is inverted.

Tail range has no upper bound and is relative to the newest messages, such as -50:.

Absolute range uses concrete bounds, such as 150:250.

Overlap is the set of message indices present in both the old and new loaded ranges.

Viewport anchor identifies a visible message index and its viewport-relative offset.

Pinned to bottom means the viewport is within the platform's configured threshold of the newest loaded content and is eligible for normal tail following.

Baseline behavior

Initial and persisted ranges

A newly opened chat defaults to the final 50 session messages.
The selected range is scoped to the connection and session.
A previously persisted range may replace the default when the chat is restored.
Users may continue to enter an arbitrary Python-style range through the existing message-range settings surface.

Loaded-range controls

The transcript exposes contextual actions where they can change the loaded range:

Show older loads an earlier overlapping window.
Show newer loads a later overlapping window.
Show all clears both range bounds.
Show last 50 selects the final 50 messages.

Older and show-all actions belong at the visual top. Newer and show-last actions belong at the visual bottom. An inapplicable action is absent, and a range action cannot be invoked while another message load is in progress.

Ordinary range navigation uses pages of 50 messages and keeps at most 100 messages loaded before sliding a bounded window. Show-all is an explicit exception to that ordinary bound.

Viewport controls

Scroll-to-top and scroll-to-bottom change only the viewport. They do not load messages outside the current range.

Scroll-to-top reaches the oldest loaded content.
Scroll-to-bottom reaches the newest loaded content.
A control is absent when its destination is already within the platform's edge threshold.
Explicit edge navigation is bounded, can be superseded by later user input, and must converge on the actual loaded edge rather than merely issuing one best-effort native scroll command.

Position preservation

When older or newer range navigation retains messages that were visible before the load, the frontend preserves the user's place:

one overlapping visible message is selected as the operation's viewport anchor before replacing the loaded data;
after the new range is rendered, that same message index is restored at approximately the same viewport-relative offset;
the frontend does not default to the top or bottom of the new range while a valid overlap anchor remains available.

Show-last intentionally returns to the newest edge. Behavior for show-all and arbitrary range changes is not yet normalized beyond retaining any behavior explicitly selected by those actions.

Tail following

New content may follow the viewport while the transcript is pinned to the bottom. Manual movement or explicit navigation away from the bottom detaches that affinity. Streaming or rendering updates must not pull a detached user back to the bottom. Explicit bottom navigation restores bottom affinity after arrival.

Acceptance examples

Expanding a tail range

If messages 175 through 224 are loaded by -50:, Show 50 older selects -100:. A visible overlapping message remains at approximately its previous screen position after messages 125 through 224 render.

Moving beyond the bounded tail

If the final 100 messages are already loaded and earlier messages exist, another older action selects an absolute 100-message window with a 50-message overlap. Repeated navigation slides that bounded window toward the start of history.

Moving toward newer history

From 150:250, Show 50 newer first expands or slides the loaded window toward newer indices. When the requested absolute range reaches the end of history, the frontend returns to an appropriate tail range.

From the middle of a loaded transcript, scroll-to-top reaches the oldest loaded row without fetching earlier messages. Scroll-to-bottom then reaches the newest loaded row and restores bottom affinity.

Detached streaming

If the user scrolls away from the newest loaded message while an answer is streaming, subsequent chunks do not take control of the viewport. The user can explicitly return with scroll-to-bottom.

Baseline non-goals

Previous or next user-message navigation.
Direct navigation to an arbitrary message index.
A lightweight session-wide message index or preview response.
Stable message identity independent of session-history position.
One shared native scroll implementation.
Automatic replacement of show-all for very large histories.