Fix resume waiter leaks and long-session TUI stalls

[zhnt]

Summary

• Cancel the pending terminal render waiter when input returns or is cancelled, preventing the Python 3.14 Event.wait() task warning after resume.
• Defer synchronous context-usage refresh until the active TUI run completes so Bash tool execution does not pause Working animation or input.
• After compaction, avoid rebuilding a pre-compaction model request for provider-usage display. Reuse the already replayed context when counting messages.

Validation

• 63 focused Harness, transcript, compaction, model-call, and Coding session tests passed on local main.
• Focused TUI and Coding TUI playback tests passed during the original fixes.
• Ruff check passed for the changed Harness files; git diff --check origin/main..main passed.
• Local make check-changed passed docs and architecture checks, then was stopped during its long Coding suite. The selected GitHub checks are the merge gate.

Contract notes

AgentTranscriptInspector.message_counts() now accepts an optional prebuilt message sequence. Existing callers remain compatible. No configuration changes.