fix: add on_memory_write bridge to sequential tool execution path

[teknium1]

Summary

Fixes #10174 — The on_memory_write bridge that notifies external memory providers (ClawMem, retaindb, supermemory, holographic, etc.) was only present in the concurrent tool execution path (_invoke_tool, line ~7018). The sequential path (_execute_tool_calls_sequential, line ~7459) — which handles all single tool calls — was missing it entirely.

Since single-call memory writes are the common case (the model typically calls memory alone, not in parallel with other tools), this meant external memory providers silently missed the vast majority of memory operations.

Fix

Added the identical bridge block to the sequential path's memory handler (10 lines, exact mirror of the concurrent path):

# Bridge: notify external memory provider of built-in memory writes
if self._memory_manager and function_args.get("action") in ("add", "replace"):
    try:
        self._memory_manager.on_memory_write(
            function_args.get("action", ""),
            target,
            function_args.get("content", ""),
        )
    except Exception:
        pass

Tests

4 new tests in TestOnMemoryWriteBridge:

• test_on_memory_write_add — fires for add actions
• test_on_memory_write_replace — fires for replace actions
• test_on_memory_write_remove_not_bridged — documents the add/replace-only contract
• test_on_memory_write_tolerates_provider_failure — one bad provider doesn't block others