Python: Preserve non-adjacent function call/result pairs during compaction

[jstar0]

Motivation & Context

Compaction currently groups only contiguous message spans. When approval or
resume traffic separates an assistant function_call declaration from its tool
function_result, each half receives a different group id. Group-based
strategies can then retain the result while excluding the declaration, producing
provider-invalid model input.

This change keeps non-adjacent call/result pairs atomic without changing the
behavior of pending, unmatched, malformed-order, or ambiguous duplicate calls.

Description & Review Guide

• What are the major changes? Link result spans to a unique earlier
  declaration span with the same call_id, share the declaration's group id,
  group index, and reasoning metadata, and rewind incremental annotation when a
  matching result is appended later. Regression coverage includes truncation,
  multiple calls, combined result messages, ambiguous ids, and incremental
  append state.
• What is the impact of these changes? Existing group-based compaction
  strategies now preserve valid function call/result pairs even when unrelated
  messages separate them. Hosted and MCP tool grouping, public APIs, and
  individual compaction strategies are unchanged.
• What do you want reviewers to focus on? The unique-call_id linking rules,
  especially the intentional fallback to existing grouping for ambiguous or
  malformed sequences, and the incremental re-annotation boundary.

Verification:

uv run pytest packages/core/tests/core/test_compaction.py packages/core/tests/core/test_harness_memory.py -q
uv run poe syntax
uv run poe test -A -m "not integration"
uv run pyright packages/core/agent_framework/_compaction.py packages/core/tests/core/test_compaction.py
uv run ty check packages/core/tests/core/test_compaction.py

Related Issue

Fixes #7212

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) - a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

This PR fixes a compaction-grouping bug in the Python core where non-adjacent assistant function_call declarations and tool function_result messages could end up in different groups, allowing group-based strategies to orphan one half and produce provider-invalid model inputs. It extends grouping to pair spans by unique call_id (without changing existing adjacency behavior for ambiguous/invalid cases) and updates incremental annotation so late-appended results rewind to the matching declaration group.

Changes:

• Add a post-pass in group_messages to link non-adjacent function result spans to a unique earlier declaration span with the same call_id, sharing group_id and reasoning metadata.
• Update incremental annotation to rewind the re-annotation window to the unique declaration group when a matching result is appended later, and ensure group indices remain collision-free with linked/non-contiguous groups.
• Add regression tests covering non-adjacent pairing, multi-result/combined-result scenarios, ambiguous duplicates, incremental append behavior, and truncation atomicity.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/_compaction.py	Implements call-id-based linking of non-adjacent function call/result spans and adjusts incremental re-annotation/group index handling to keep linked pairs atomic.
python/packages/core/tests/core/test_compaction.py	Adds targeted regression tests validating non-adjacent pairing, ambiguity rules, incremental extension behavior, and truncation atomicity for tool call/result pairs.

[eavanvalkenburg]

please make sure to use the defined PR template @jstar0

[jstar0]

Updated the PR body to use the repository template, including Motivation & Context, Description & Review Guide, Related Issue, verification, and the contribution checklist.

[eavanvalkenburg]

@jstar0, thank you for the non-adjacent function call/result compaction fix. I incorporated your changes into the consolidated draft PR #7345 and preserved your commit attribution there. Closing this PR in favor of the consolidated work.