Validate set_color_depth input in the Python tracker

[snowplow-claude-review]

🤖 Draft implementation — refinement loop (3a307af295a281a9ba70f6d2fa691c78)

Drafted automatically by the Snowplow refinement loop (refine → product review → implement → review) from a Notion refinement, and opened here for a human to finish.

Heads-up: this is a starting point. A human reviewer should verify, finish, and run CI before merging.

What the loop did

Validate set_color_depth input in the Python tracker

What changed

Added greater_than(depth, 0) validation to Subject.set_color_depth in snowplow_tracker/subject.py, placed immediately before the assignment to standard_nv_pairs["cd"]. The greater_than contract helper was already imported on line 19 — no new imports or error-handling patterns introduced.

Updated the depth docstring type annotation from int to int,>0 to match the style of the sibling setters (set_screen_resolution, set_viewport).

Added test_set_color_depth_validation to TestSubject in snowplow_tracker/test/unit/test_subject.py:

• Asserts ValueError for 0 and -1
• Confirms positive values (24) still work and are stored correctly

All 4 existing subject tests continue to pass (test_subject_0, test_combine_subject, etc.).

Why

set_screen_resolution and set_viewport already guard their numeric inputs with greater_than, but set_color_depth was never given the same treatment. Zero and negative colour-depth values are nonsensical and would silently produce invalid events. This is a consistency fix — no wire-format or schema change; the cd field itself is unchanged.

Decisions

• Reused the existing greater_than contract helper (no new error handling invented).
• No change to any other Subject setter — out of scope by design.
• No schema or wire-format change — only invalid inputs now raise at the SDK boundary.

Reviewer checklist

• greater_than(depth, 0) is placed before the assignment in set_color_depth, consistent with sibling setters
• Test covers both invalid inputs (0, -1) and a valid one (24)
• Existing tests still pass (test_subject_0, test_combine_subject)
• No unintended changes to other setters or to the event payload format

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[Coveralls (coveralls)]

coverage: 96.63% (+0.01%) from 96.619% — loop/3a307af295a281a9ba70f6d2fa691c78-snowplow-python-tracker-29727716248 into master