fix(a2a): join appended streaming chunks without spaces

[parthiban-sivakumar]

Related issue

Fixes #7473

Summary

When an A2A agent streams its reply in small chunks, CrewAI joined the chunks with a space. So "Hello, world!" came back as "Hel lo, wor ld !".

Each chunk comes as an artifact update with append=True. Now the streaming handler checks this flag. If append is true, the text is added to the same artifact's text with no space. Different artifacts are still joined with a space like before, so normal replies do not change.

The change is in one helper, process_artifact_update in streaming/params.py. It is used in the main stream loop and also in the reconnect path, so chunks that come after a reconnect are joined correctly too.

Verification

• Tests added or updated for the changed behavior
• Relevant tests and quality checks pass locally

I added tests/a2a/test_streaming_artifact_text.py with 4 tests:

• the chunks from the issue come back as "Hello, world!"
• two separate artifacts still have a space between them
• two artifacts streamed at the same time each keep their own text
• chunks after a reconnect continue the same text

Three of these tests fail on main and pass with this change. The script from the issue now prints Hello, world!. The full lib/crewai/tests/ suite passes (5475 passed, 43 skipped), and ruff and mypy are clean.

Additional context

This PR only fixes streaming. Polling and push notifications also join parts with a space, but there the finished artifact does not tell us which parts were streamed chunks, so I did not change them here.

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Reviewing files that changed from the base of the PR and between b7da574 and 07f4037.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/a2a/updates/streaming/params.py
• lib/crewai/tests/a2a/test_streaming_artifact_text.py

🚧 Files skipped from review as they are similar to previous changes (2)

• lib/crewai/tests/a2a/test_streaming_artifact_text.py
• lib/crewai/src/crewai/a2a/updates/streaming/params.py

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📝 Walkthrough

Walkthrough

The streaming handler now tracks text positions by artifact. Appended text chunks are concatenated without separators during live streaming and recovery. Tests cover separate artifacts, interleaved updates, replacement updates, and updates received after reconnection.

Changes

Artifact text reassembly

Layer / File(s)	Summary
Artifact update processing lib/crewai/src/crewai/a2a/updates/streaming/params.py	Adds process_artifact_update, which joins text parts, concatenates appended text for known artifacts, records new artifact positions, and replaces text for non-appended updates.
Streaming integration and validation lib/crewai/src/crewai/a2a/updates/streaming/handler.py, lib/crewai/tests/a2a/test_streaming_artifact_text.py	Threads artifact positions through live streaming and recovery paths. Tests validate contiguous chunks, separate artifacts, interleaved artifacts, replacement updates, and post-reconnect appends.

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 07f40

No merge-blocking issue is identified from the available evidence.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The changes fix the streaming path in issue #7473. process_artifact_update concatenates append=True chunks for the same artifact and preserves separation between distinct artifacts. The added test…	Apply the artifact-aware reassembly behavior to the polling and push notification paths and to wrapper.py::_handle_max_turns_exceeded, or provide evidence that those paths already satisfy issue #7473. Add automated coverage for appended c…
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: joining appended A2A streaming chunks without unwanted spaces.
Description check	✅ Passed	The description includes the related issue, explains the cause and solution, documents verification and test results, and provides additional context about out-of-scope polling and push notification p…
Out of Scope Changes check	✅ Passed	The changed streaming handler, artifact-position helper, recovery logic, and tests directly support the streaming reassembly objective in issue #7473. The supplied evidence shows no unrelated product …

Full details: Linked Issues check

Explanation

The changes fix the streaming path in issue #7473. process_artifact_update concatenates append=True chunks for the same artifact and preserves separation between distinct artifacts. The added tests cover normal streaming, interleaved artifacts, replacement, and reconnect handling. Issue #7473 also identifies the shared task-state reassembly used by polling and push notifications, plus the max-turns fallback in wrapper.py. The supplied change summary shows no changes to those paths. Their compliance is therefore not established, and the linked issue remains only partially implemented.

Resolution

Apply the artifact-aware reassembly behavior to the polling and push notification paths and to wrapper.py::_handle_max_turns_exceeded, or provide evidence that those paths already satisfy issue #7473. Add automated coverage for appended chunks and separate artifacts in each affected path.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

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Actionable comments posted: 1

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Inline comments:
In `@lib/crewai/src/crewai/a2a/updates/streaming/params.py`:
- Around line 29-57: Update process_artifact_update so a non-appended update for
an artifact with an existing artifact_positions entry replaces
result_parts[position] rather than appending a new entry. Preserve the recorded
position for replacement, while retaining the current append=True concatenation
and new-artifact behavior.

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ℹ️ Review info

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Configuration used: Organization UI

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Plan: Advanced

Run ID: 9db92132-b33a-4fe7-8454-2852cbd22628

📥 Commits

Reviewing files that changed from the base of the PR and between c6ff786 and da5e0c0.

📒 Files selected for processing (3)

• lib/crewai/src/crewai/a2a/updates/streaming/handler.py
• lib/crewai/src/crewai/a2a/updates/streaming/params.py
• lib/crewai/tests/a2a/test_streaming_artifact_text.py

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[parthiban-sivakumar]

@Vidit-Ostwal the 3 failing tests in this run are tests/llms/azure/test_azure_responses.py::TestAzureResponsesProperties. This PR only changes A2A streaming files, so I do not think they are related.

I ran them locally on this branch: the file alone passes (25 passed), the whole tests/llms/azure folder passes (108 passed), and CI's own split (--splits 8 --group 5) on Python 3.10 also passes. Could you please re-run the job?

[VANDRANKI]

Community review, not a merge-gate approval.

I traced process_artifact_update in lib/crewai/src/crewai/a2a/updates/streaming/params.py against all 5 new tests by hand, plus confirmed the final assembly point: handler.py line ~643 does result=" ".join(result_parts) if result_parts else "". That's the key fact that makes the fix's design make sense: each entry in result_parts is one artifact's accumulated text, joined with a space against every other artifact at the very end, while within one artifact's entry, appended chunks are now concatenated with "".join(texts) (no separator). The old code did result_parts.extend(part.root.text for part in artifact.parts if part.root.kind == "text"), which put every chunk of every artifact update into its own slot in result_parts, so a server streaming one reply as ["Hel", "lo, ", "wor", "ld", "!"] would come back as "Hel lo, wor ld !" after the final space-join, since the join can't tell a mid-word chunk boundary from a real artifact boundary.

The new artifact_positions: dict[str, int] fixes that by remembering which slot in result_parts belongs to which artifact_id. I walked through each test:

• test_appended_chunks_are_joined_without_spaces: 5 chunks, same artifact, first append=False then rest append=True. Traces to a single result_parts entry built by concatenation, giving exactly "Hello, world!".
• test_interleaved_artifacts_append_to_their_own_text: two different artifact IDs interleaved (greeting, subject, greeting, subject), each with its own append chunk. Traces to two independent slots that never cross-contaminate, joined with one space at the end: "Hello World".
• test_an_update_without_append_replaces_the_artifact_text: a third update to the same artifact with append=False after two appends correctly hits the elif update.append / else branch's else, replacing the slot outright (result_parts[position] = ...) rather than appending, matching the docstring's claim that this mirrors a2a.utils.append_artifact_to_task replacing an artifact of the same ID.
• test_chunks_after_a_reconnect_continue_the_same_text is the one I checked most carefully, since it depends on state surviving an interruption: the diff threads a new artifact_positions parameter into _try_recover_from_interruption alongside result_parts, and both call sites in execute() pass the same live dict through (artifact_positions=artifact_positions). So a reconnect's resubscribed chunks still find the pre-disconnect artifact's position and append to it rather than starting a fresh, disconnected entry. I confirmed both execute() call sites of _try_recover_from_interruption were updated with this new argument, not just one.

I did not check every other caller of process_status_update (the sibling function in the same file) for a similar issue, this review is scoped to the artifact-text path the diff actually changes. Within that scope, the logic is correct and the test suite specifically targets the boundary cases (interleaving, replace-vs-append, reconnect) rather than just the straightforward case.