[Angnuo (angnuoli)]

Description

Fix two chat rendering problems exposed by long, tool-heavy conversations: earlier user messages disappear from the loaded timeline, and a large blank gap appears before the final answer.

Changes

• Follow Gateway history pagination using older cursors or next offsets instead of stopping after the latest 200 records.
• Keep the latest runtime snapshot and reject non-advancing pagination or transcript/session changes.
• Render only assistant bubbles with visible content, while retaining grouped reasoning/tool panels and original message indexes for editing.
• Add regression coverage for multi-page history, pagination safety, empty bubbles, mixed content, and user-message editing.

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Testing

• Main-process focused tests: vitest run src/gateway-client.test.ts src/chat-run-lifecycle.test.ts (75 passed).
• Full renderer suite: vitest run (1,036 passed, 2 skipped).
• Main-process type check: tsc --noEmit.
• Renderer type check: vue-tsc --noEmit -p tsconfig.json.
• Prettier and git diff --check.
• Scoped ESLint checks (no errors; existing warnings only).
• Manual application testing / installer rebuild (not performed).

Checklist

• Self-reviewed the patch.
• Added regression tests that reproduce both reported symptoms.
• Limited the PR to the five chat-related files; unrelated local changes are excluded.