Adds a `modify` response type to pre_tool_call hooks so a hook can
transform tool arguments before the tool executes, instead of repairing
results afterwards via post_tool_call.
- hermes_cli/plugins.py: _dispatch_pre_tool_call_hooks() fires hooks once
and returns (block_message, modified_args); modify directives
shallow-merge into an accumulated dict built from the original args.
- agent/shell_hooks.py: _parse_response() accepts both the canonical
{"action": "modify", "args": {...}} and Claude Code-compatible
{"decision": "modify", "tool_input": {...}} wire formats.
- model_tools.py, agent/tool_executor.py, agent/agent_runtime_helpers.py:
dispatch sites migrated; modified args applied before execution.
- Docs + 10 new tests (merge semantics, precedence, block interplay).
Salvaged from PR #28953. Best fix for #18988.
d083b85591