Python: Implement annotation-based context compaction (#4469)

* Implement annotation-based context compaction

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Handle missing compaction attributes in BaseChatClient

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix CI typing and bandit issues

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Optimize incremental compaction annotation pass

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refinement

* Python: add ToolResultCompactionStrategy and CompactionProvider

Add ToolResultCompactionStrategy that collapses older tool-call groups
into short summary messages (e.g. [Tool calls: get_weather]) while
keeping the most recent groups verbatim. This mirrors the .NET
ToolResultCompactionStrategy from PR #4533.

Add CompactionProvider as a context-provider that auto-applies compaction
before each agent turn and stores compacted history in session state
after each turn.

Includes tests and samples for both features.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refinement and alignment with dotnet PR

* updated tool result compaction

* updated tool result compaction

* Python: add ToolResultCompactionStrategy, CompactionProvider, and skip_excluded

- ToolResultCompactionStrategy collapses older tool-call groups into
  [Tool results: func_name: result] summaries with bidirectional tracing
  (same pattern as SummarizationStrategy).
- CompactionProvider as BaseContextProvider with separate before_strategy
  and after_strategy parameters. before_strategy compacts loaded context;
  after_strategy compacts stored history via history_source_id.
- InMemoryHistoryProvider gains skip_excluded flag to filter out messages
  marked as excluded by compaction strategies.
- Tests, samples, and exports updated.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fixed checks

* fix mypy

* Fix: ensure summary messages from both strategies get full compaction annotations

SummarizationStrategy was not calling annotate_message_groups after
inserting its summary message, so the summary lacked core group
annotations (id, kind, index, has_reasoning, _excluded). Added the
missing call. ToolResultCompactionStrategy already had it.

Added tests verifying both strategies produce fully annotated summaries.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* updated propagation

* fix mypy

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/samples/02-agents/compaction/README.md

@@ -0,0 +1,23 @@
+# Context Compaction Samples
+
+This folder demonstrates context compaction patterns introduced by ADR-0019.
+
+## Files
+
+- `basics.py` — builds a local message list and applies each built-in strategy one at a time.
+- `advanced.py` — composes multiple strategies with `TokenBudgetComposedStrategy`.
+- `agent_client_overrides.py` — shows client defaults, agent-level overrides, and per-run compaction overrides.
+- `custom.py` — defines a custom strategy implementing the `CompactionStrategy` protocol.
+- `tiktoken_tokenizer.py` — shows a `TokenizerProtocol` implementation backed by `tiktoken`.
+- `compaction_provider.py` — uses `CompactionProvider` with an agent and `InMemoryHistoryProvider`.
+
+Run samples with:
+
+```bash
+uv run samples/02-agents/compaction/basics.py
+uv run samples/02-agents/compaction/advanced.py
+uv run samples/02-agents/compaction/agent_client_overrides.py
+uv run samples/02-agents/compaction/custom.py
+uv run samples/02-agents/compaction/tiktoken_tokenizer.py
+uv run samples/02-agents/compaction/compaction_provider.py  # requires OPENAI_API_KEY
+```