fix: track all tool invocations in ToolMetrics instead of overwriting

[giulio-leone]

Problem

ToolMetrics.add_call() overwrites self.tool with the latest invocation on every call (line 142: self.tool = tool). When users inspect AgentResult.metrics.tool_metrics, they can only see the last call's toolUseId and input — all previous invocations are lost.

This means to_dict() / get_summary() only expose the final tool call's data, making it impossible to audit which inputs were passed across multiple invocations of the same tool.

Closes #301

Solution

• Added invocations: list[ToolUse] field to ToolMetrics that accumulates every call
• Updated add_call() to append each tool invocation to the list
• Updated to_dict() to expose an invocations array with all tool_use_ids and input_params
• Backwards compatible: self.tool is still updated to the latest invocation — existing code reading metrics.tool continues to work

Changes

• src/strands/telemetry/metrics.py: Added invocations field, updated add_call() and to_dict()
• tests/strands/telemetry/test_metrics.py: Updated existing tests + 2 new tests for invocation tracking

Testing

• All 1888 tests pass (1866 core + 22 telemetry)
• New tests verify:
  • Multiple invocations are tracked with correct inputs
  • get_summary() includes full invocations array
  • Backwards compatibility (.tool still points to latest)

[giulio-leone]

Friendly ping — fixes ToolMetrics to track all tool invocations instead of overwriting previous entries, giving accurate metrics for multi-tool calls.

[giulio-leone]

Rebased this branch onto the latest main and force-pushed it.

Local validation I ran:

• .venv/bin/python -m pytest tests/strands/telemetry/test_metrics.py::test_tool_metrics_tracks_all_invocations tests/strands/telemetry/test_metrics.py::test_tool_metrics_invocations_in_summary -q -> 2 passed

Real branch-vs-main proof (using the repo venv and explicit PYTHONPATH=<checkout>/src so the imported module path is unambiguous):

• main imported sdk-python-main/src/strands/telemetry/metrics.py
  • call_count=3
  • latest_tool_use_id=id3
  • has_invocations_attr=False
  • invocation_count=0
  • summary_invocations=[]
• this branch imported sdk-python/src/strands/telemetry/metrics.py
  • call_count=3
  • latest_tool_use_id=id3
  • has_invocations_attr=True
  • invocation_count=3
  • summary_invocations=[{"input_params":{"city":"Berlin"},"tool_use_id":"id1"},{"input_params":{"city":"Paris"},"tool_use_id":"id2"},{"input_params":{"city":"Rome"},"tool_use_id":"id3"}]

So the rebased branch preserves backwards compatibility (tool still points to the latest invocation) while fixing the real telemetry gap: repeated calls to the same tool now retain the full invocation history instead of silently overwriting it.

[giulio-leone]

Refreshed this branch onto current main and revalidated it on the rebased head.

Repo-native gate (run twice with no code changes between passes):

• uv run hatch run test-format
• uv run hatch run test-lint
• uv run hatch run test -- tests/strands/telemetry/test_metrics.py -q

Results on refreshed head d3c02e483ba1b987c1222c9f1a46e16325ebdb23:

• ruff check: pass
• mypy ./src: pass (Success: no issues found in 140 source files)
• tests/strands/telemetry/test_metrics.py: pass (22 passed)

Direct branch-vs-main proof on exact source trees used the same temporary proof_1892_tool_metrics_invocations.py in both checkouts and asserted three things:

1. ToolMetrics retains the full invocation history across repeated calls.
2. EventLoopMetrics.get_summary() exposes the full invocation list.
3. Backwards compatibility is preserved because .tool still points at the latest invocation.

Proof result:

• Refreshed branch: 3 passed
• Current main (fd8168a531c140a0082a3c6412a577fe81db21f0 at verification time): 2 failed, 1 passed

The current main failures are the exact telemetry gap this PR fixes:

• ToolMetrics still has no invocations history (getattr(..., "invocations", None) == None after 3 calls).
• EventLoopMetrics.get_summary() still omits the invocations array entirely (KeyError: 'invocations').
• The compatibility control still passes on both trees, so .tool still tracks the latest invocation exactly as before.