fix(cli): preserve intra-turn text/tool order for ACP sessions

[junmo-kim]

Problem

When using hapi gemini (ACP backend), text chunks that arrive before a
tool call are rendered after all tool blocks in the web UI. A session
producing text → tool_call → tool_result → text arrives at the Hub and
Web in the order tool_call, tool_result, text, so the assistant's
reasoning appears below the tool output rather than above it.

This is an intra-turn ordering issue — distinct from the turn-completion
timing addressed in #356.

Solution

AcpMessageHandler.handleUpdate now calls flushText() immediately
before dispatching a tool_call or plan update — a new tool
invocation or plan closes the preceding text segment.

tool_call_update (tool result / progress) does NOT flush: it is a
lifecycle event on an already-open tool call, not a boundary between
text segments. Flushing there would split a text segment that spans
the tool's execution and break the cumulative-delta dedup inside
appendTextChunk.

The cumulative-delta dedup, audience filtering, rate-limit parsing,
and internal-event suppression in AcpMessageHandler are untouched.
AcpSdkBackend's waitForSessionUpdateQuiet / turn_complete logic
is not modified.

Tests

• The old ordering test is replaced by an equivalent case asserting
  ['text', 'tool_call', 'tool_result'].
• Interleave scenarios: text → tool and text → tool → text → tool.
• Dedup-across-boundary: cumulative dedup still works inside each text
  segment separated by tool events.
• Regression: text streamed between tool_call and tool_call_update
  is preserved and emitted after tool_result, not duplicated or
  fragmented.
• All other existing tests (audience filter, rate-limit, internal-
  event, overlap dedup) are unchanged and pass.

[github-actions]

Findings

• No actionable findings on the added/modified lines.

Summary

• Review mode: initial
• No diff-attributable correctness, security, or regression issues found in the latest PR diff.
• Residual risk/testing gap: not run in automation here; coverage is strong for text -> tool_call -> tool_result ordering and dedup boundaries, but I did not verify against a live ACP provider stream.

Testing

• Not run (automation)

HAPI Bot