PR #43861: fix(gateway): stop deduplicating repeated characters in streaming deltas

• Repository: openclaw/openclaw
• Author: duoduoart
• State: open | merged: False
• Link: https://github.com/openclaw/openclaw/pull/43861

Description (problem / solution / changelog)

Problem

When streaming text with repeated characters (e.g. 999999999999), the TUI displays only the first occurrence (e.g. 9). Reopening the TUI loads the correct result from session history.

Root Cause

appendUniqueSuffix() in src/gateway/server-chat.ts tries to detect overlapping text between the tail of accumulated text and the head of a new streaming delta. When the delta contains characters that match the end of the existing text, it incorrectly treats them as "overlap" and deduplicates:

base = "9",  suffix = "9"  → base.endsWith(suffix) → true → returns "9" (should be "99")
base = "99", suffix = "9"  → overlap "9" detected   → returns "99"  (should be "999")

This means streaming 9 * 111111111111 = 999999999999 one token at a time collapses to just "9".

Fix

Replace the overlap detection with simple concatenation. Streaming deltas from providers (OpenAI-compatible, Anthropic, etc.) are purely incremental and never overlap with previously emitted content. The overlap detection was a defensive measure that caused more harm than good.

Tests

• 9 new unit tests for appendUniqueSuffix covering single-char, multi-char, and word-level repeated deltas
• All 23 existing server-chat.agent-events integration tests pass
• All 199 TUI tests pass

AI Disclosure

This PR was authored with AI assistance (OpenClaw/Claude). Changes reviewed and tested locally.

Fixes #43828

Changed files

• src/gateway/server-chat.append-delta.test.ts (added, +56/-0)
• src/gateway/server-chat.ts (modified, +15/-11)