fix(vscode): improve long-session prompt navigation

[marius-kilocode]

Long sessions can contain more prompts than the rail can display, while restored sessions initially expose only their newest message pages. The rail previously kept only the newest prompts without showing that earlier navigation targets were missing, so users could not reliably return to the beginning of a conversation.

This keeps the rail compact without making history disappear. Tick capacity now follows the actual tick spacing instead of the much taller preview rows, while the bounded navigator exposes every loaded prompt and virtualizes large lists. Scrolling upward loads earlier pages automatically, and the First prompt action progressively loads the remaining history before jumping. Stable row-key lookup continues to use Virtua without mounting intervening transcript rows.

Opening the navigator does not fetch history by itself. Paging remains tied to explicit scroll or First prompt intent, and a lightweight loading row preserves position while older prompts are prepended.

Earlier history available

The restored session has 240 of 524 messages loaded. The leading history marker communicates that earlier prompts are still available.

Complete history

After loading all 524 messages, the rail represents the complete prompt history while the navigator and transcript remain virtualized.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Incremental review since 5ebc3d7: only MessageList.tsx changed. Both previously flagged issues in this file are resolved:

• The pending-jump effect now falls back to a data-row-key DOM query and scrollIntoView for non-virtualized rows, matching jump()'s own fallback path.
• The "First prompt" progressive load, on making no further progress (historyAction returns stop), now jumps to the earliest currently-loaded prompt instead of silently doing nothing.

The previously flagged prompt-rail.ts:116 capacity-gate issue is unrelated to this diff (file unchanged) and remains open as a separate comment.

Files Reviewed (1 file)

• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx - 2 previously flagged issues resolved

Previous Review Summary (commit 5ebc3d7)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 5ebc3d7)

Status: 3 Issues Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	0
SUGGESTION	3

Issue Details (click to expand)

SUGGESTION

File	Line	Issue
packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx	992	Pending jump resolution never retries the DOM fallback for non-virtualized (direct) rows, so it can get stuck
packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx	1065	"First prompt" progressive load gives up silently with no user feedback when a page makes no progress
packages/kilo-vscode/webview-ui/src/components/chat/prompt-rail.ts	116	At capacity === 1 with unloaded history, the rail's >= 2 entries gate hides the entire navigator, including the history affordance

Files Reviewed (31 files)

• .changeset/long-session-prompt-navigation.md
• packages/kilo-vscode/tests/unit/prompt-rail.test.ts
• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx - 2 issues
• packages/kilo-vscode/webview-ui/src/components/chat/PromptRail.tsx
• packages/kilo-vscode/webview-ui/src/components/chat/prompt-rail.ts - 1 issue
• packages/kilo-vscode/webview-ui/src/context/session.tsx
• packages/kilo-vscode/webview-ui/src/i18n/*.ts (all 26 locales)
• packages/kilo-vscode/webview-ui/src/stories/StoryProviders.tsx
• packages/kilo-vscode/webview-ui/src/stories/chat.stories.tsx
• packages/kilo-vscode/webview-ui/src/styles/prompt-rail.css
• visual regression baseline PNGs (3, updated by CI bot commit)

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_{Reviewed by claude-sonnet-5 · Input: 30 · Output: 8.4K · Cached: 642.3K}

_{Review guidance: REVIEW.md from base branch main}