fix(pixel-teams): stream UTF-8 chunks incrementally without splitting multi-byte sequences

[vaibhavsrv]

Why this matters

In ods/extensions/services/dashboard-api/routers/pixel_teams.py, the _run(owner, agent) task consumes SSE events from _retained_chat_stream(...) via async for chunk in response.body_iterator:. For incoming byte chunks, it directly executed buffered += chunk.decode("utf-8") if isinstance(chunk, bytes) else chunk.

If a multi-byte UTF-8 character (such as emoji, symbols, or localized characters) is split across network TCP or chunk boundaries by the upstream inference stream, calling chunk.decode("utf-8") on the first chunk containing an incomplete sequence raises an unhandled UnicodeDecodeError ('utf-8' codec can't decode bytes in position ...: unexpected end of data). This abruptly crashes the agent team worker task and marks the worker as failed.

This surgical fix introduces codecs.getincrementaldecoder("utf-8")() to buffer incomplete multi-byte code units across chunk boundaries before appending decoded text to the SSE line buffer.

Validation

• Baseline reproduction: Simulated a split multi-byte character sequence (b'\xf0\x9f' in chunk 1 followed by b'\x9a\x80' in chunk 2) on unpatched pixel_teams.py; baseline immediately failed with UnicodeDecodeError.
• Post-fix behavior: Incremental decoding buffers partial code units across chunk boundaries; _run decodes the full character (🚀) without errors and emits the delta choice event.
• Telemetry: pixel-teams suites: 29 passed. New-test syntax and diff checks pass; new regressions wired into test suite.

Overlap check

• fix(pixel-settings): convert decode and protocol failures to unsafe-settings-source #5697 (fix(pixel-settings): convert decode and protocol failures to unsafe-settings-source): Hardens coordinator file decoding; zero overlap with SSE streaming in pixel_teams.py.
• fix(pixel-settings): reject active token limits exceeding provider capacity #5696 (fix(pixel-settings): reject active token limits exceeding provider capacity): Bounds runtime capability values in contract.py; zero overlap with agent team streams.
• fix(dashboard-api): tolerate evicted or missing attempts during pixel chat cancel #5695 (fix(dashboard-api): tolerate evicted or missing attempts during pixel chat cancel): Touches dashboard API chat result store lifecycle; zero overlap with agent team SSE decoding.
• fix(pixel-teams): safely ignore non-conforming or corrupted team history files #5689 (fix(pixel-teams): safely ignore non-conforming or corrupted team history files): Touched team history JSON loading; this PR addresses HTTP chunk streaming without conflicts.

Risk / AI disclosure

AI-assisted investigation, implementation and CLI regressions. This uses Python's standard incremental UTF-8 decoder during SSE chunk buffering and does not alter downstream SSE event parsing or contract schemas. Independent human review and platform/runtime qualification remain gates. No running configuration, deployment or upstream merge changed.

Follow-up integration evidence

Composed with #5697 at 8b9f0e2e3 without conflicts. Production and test diffs passed together; team coordinator and streaming checks remain intact.
Backlog composition was local-only (production/test diffs, excluding workflow/Makefile wiring); it is not an upstream merge or independent human approval. Declared live-review gates remain open.