docs(error): replace phantom FORMAT_INCOMPATIBLE with UNSUPPORTED_FEATURE in create_media_buy

[bokelley]

Closes #4852

FORMAT_INCOMPATIBLE appeared in the error table and two JSON examples in docs/media-buy/task-reference/create_media_buy.mdx but was never present in static/schemas/source/enums/error-code.json. Any SDK that validates errors[].code against the published enum would treat seller responses using this code as unknown — falling back to unstructured recovery, which defeats the point of the error vocabulary. Replaced with UNSUPPORTED_FEATURE (the code already used for the v2/capability_ids[] path) so the v1 and v2 format-mismatch paths use the same code with identical recovery semantics. The FORMAT_INCOMPATIBLE table row was removed and its v1-path guidance folded into the existing UNSUPPORTED_FEATURE row to avoid two rows with the same code causing agent-parseability ambiguity. field paths in both v1 JSON examples updated to packages[0].format_ids[0] (element-level) for consistency with the v2 example's packages[0].capability_ids[0].

Non-breaking justification: docs-only change. FORMAT_INCOMPATIBLE was never in the published enum, so no consumer could have been conformantly using it; removing it from docs and replacing with the valid UNSUPPORTED_FEATURE code closes the divergence without any schema delta. Existing clients unaffected.

Known follow-up (out of scope): Three other error codes in the same table — TARGETING_TOO_NARROW, INVALID_PRICING_OPTION, CREATIVE_ID_EXISTS — are also absent from error-code.json. Separately tracked phantom-code sweep is the right vehicle; kept out of scope per #4852.

Pre-PR review:

• code-reviewer: approved — all blockers resolved; both v1 examples now use UNSUPPORTED_FEATURE with packages[0].format_ids[0]; no new issues
• docs-expert: approved — FORMAT_INCOMPATIBLE fully removed; v1/v2 field paths consistent; phantom-code removal is correct and complete

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See #3121
for context.

Session: https://claude.ai/code/session_01MVUhgB3tVFtW85wDQ1MATy

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Generated by Claude Code

[aao-release-bot]

LGTM. Phantom enum value removed from docs; v1 and v2 mismatch paths now share UNSUPPORTED_FEATURE, which is what makes the error vocabulary load-bearing for SDK consumers in the first place.

Things I checked

• FORMAT_INCOMPATIBLE is genuinely absent from static/schemas/source/enums/error-code.json (0 matches). UNSUPPORTED_FEATURE is present in enum (L22), enumDescriptions (L104), and enumMetadata (L229). The PR's premise is sound.
• PR head has no FORMAT_INCOMPATIBLE residue anywhere in create_media_buy.mdx.
• Single UNSUPPORTED_FEATURE table row at L921 covers both v1 (format_ids[]) and v2 (capability_ids[]) paths — no duplicate-code agent-parseability ambiguity.
• Both v1 JSON examples (L933, L1044) use field: packages[0].format_ids[0], element-level, matching the v2 example's packages[0].capability_ids[j] pattern. The field-path normalization is the right shape.
• No static/schemas/source/** change, so schema-vs-docs coherence audit and major changeset rule don't fire. Changeset is a docs-only entry (empty frontmatter, prose-only) — appropriate for a docs PR.

Follow-ups (non-blocking — file as issues)

• The PR body flags three more phantom codes in the same table (TARGETING_TOO_NARROW, INVALID_PRICING_OPTION, CREATIVE_ID_EXISTS) absent from error-code.json. Kept out of scope per #4852, but the phantom-code sweep is worth running across all task-reference pages, not just create_media_buy. Same defect class — docs ship error codes that aren't in the published enum, SDKs treat them as unknown.

Safe to merge.

[aao-release-bot]

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