feat: API Server - Pipeline runs - Mirror Pipeline Run Annotations when creating a new pipeline run

[yuechao-qin]

TL;DR

Closes https://github.com/Shopify/oasis-backend/issues/221

User-provided annotations are now mirrored into the PipelineRunAnnotation table at pipeline run creation time, and set_annotation now applies truncation and None-to-empty-string coercion via a shared helper.

What changed?

• Introduced _mirror_single_annotation, a helper that centralizes annotation write logic: guards against system-key prefix collisions, coerces None values to empty strings, truncates values to the VARCHAR max length, and upserts the row.
• Introduced _mirror_pipeline_run_annotations, which iterates over a user-supplied annotations dict and delegates each entry to _mirror_single_annotation.
• _mirror_system_annotations now accepts an optional annotations dict and calls _mirror_pipeline_run_annotations so user annotations are persisted alongside system annotations at creation time.
• create passes annotations through to _mirror_system_annotations.
• set_annotation now delegates to _mirror_single_annotation instead of directly constructing and merging a PipelineRunAnnotation, gaining truncation and coercion for free.
• The previously documented known failure for set_annotation overflowing the VARCHAR column is resolved — long values are now silently truncated rather than raising an IntegrityError.

How to test?

Run the updated test suite:

uv run pytest tests/test_api_server_sql.py

Why make this change?

Previously, user-provided annotations passed to create were not written to the PipelineRunAnnotation table, making them invisible to filter queries. Additionally, set_annotation lacked the same truncation and coercion guards applied to system annotations, causing potential IntegrityError failures on long values. Centralizing annotation write logic into _mirror_single_annotation ensures consistent behavior across all annotation write paths.

[yuechao-qin]

• feat: API Server - Pipeline runs - Mirror Pipeline Run Annotations when creating a new pipeline run #216 👈 (View in Graphite)
• master

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