fix: treat empty string cursor field as no cursor field

[devin-ai-integration]

Summary

Fixes a bug where cursor_field: [""] (list with empty string) was incorrectly treated as a valid cursor field, causing invalid SQL generation in destinations like Redshift. The error manifests as zero-length delimited identifier at or near """" when the platform serializes "no cursor configured" streams as [""] instead of [].

This PR adds defensive checks in two locations to treat empty string cursor fields as "no cursor field":

• _get_catalog_defined_cursor_field() in model_to_component_factory.py
• get_cursor_field_from_stream() in helpers.py

When an empty string cursor is detected, the code now falls back to the default cursor field defined in the manifest.

Fixes airbytehq/oncall#10700

Review & Testing Checklist for Human

• Verify the short-circuit logic is correct: not configured_stream.cursor_field must evaluate True for empty lists [] to prevent IndexError on cursor_field[0]
• Confirm that treating [""] as "no cursor" is the correct behavior (vs. raising an error)
• Note: No unit test was added for the helpers.py change - consider if this is acceptable

Suggested test plan:

1. Run the existing cursor-related tests: pytest unit_tests/sources/declarative/parsers/test_model_to_component_factory.py -k "cursor" -v
2. If possible, test with a real connection that previously failed with the empty cursor field error

Notes

• Link to Devin run: https://app.devin.ai/sessions/ab2eef614f0e42978eeec330589d7046
• Requested by: Aaron ("AJ") Steers (@aaronsteers)
• Related to PR feat(low-code cursors): Support for low-code cursors to define a field to allow for user defined cursor fields in the catalog #851 which introduced the _get_catalog_defined_cursor_field method

[devin-ai-integration]

Original prompt from API User

Comment from @aaronsteers: /ai-fix

We suspect the root cause is here. Fix there in the Python CDK if so: https://github.com/airbytehq/airbyte-python-cdk/pull/851

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Issue #10700 by @devin-ai-integration[bot]: Redshift destination failing with empty cursor field in deduplication SQL

Issue URL: https://github.com/airbytehq/oncall/issues/10700

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[github-actions]

PyTest Results (Fast)

3 821 tests  +1   3 809 ✅ +1   6m 33s ⏱️ -1s
    1 suites ±0      12 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit a4a0bac. ± Comparison against base commit 49ff36e.

[github-actions]

PyTest Results (Full)

3 824 tests   3 812 ✅  10m 56s ⏱️
    1 suites     12 💤
    1 files        0 ❌

Results for commit a4a0bac.

[Aaron ("AJ") Steers (aaronsteers)]

/prerelease

Prerelease Job Info

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Prerelease job started... Check job output.

❌ Failed to trigger prerelease workflow.
Prerelease Job Info

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Prerelease job started... Check job output.

❌ Failed to trigger prerelease workflow.

---

UPDATE from Aaron ("AJ") Steers (@aaronsteers):

PyPI had an outage at the time. Resolved now and CDK is now published: airbyte-cdk 7.6.2.post0.dev20801361583