fix(session): hide persisted reminders in resume history

[Brian Krabach (bkrabach)]

Summary

• Add one shared UI-only classifier for persisted reminder envelopes.
• Apply it to session history, replay timing, and interrupted replay remainder handling.
• Keep transcript storage and resume context unchanged; document the display-only contract.

Why

Persisted system reminders are needed for resumed context but should not appear as conversation history or consume the visible history window. Human-authored, malformed, mixed, and unflagged content remains visible.

Verification

• uv run --with truststore==0.10.4 pytest -q — 2113 passed, 1 skipped, 13 deselected, 1 xfailed.
• Deterministic DTU verification passed: real PTY amplifier session resume and --replay exited 0; fixture-backed checks covered hidden identified reminders, visible human/unflagged quotes, default-window behavior, unchanged transcript bytes, and retained resume context. This validates the fixture-shim scope; it does not claim live vendor or full default-bundle coverage.

Compatibility

No breaking changes. No provider requests, version changes, global CLI behavior, Foundation changes, or workspace-root changes.