feat(decisioning): emit UserWarning for sales-* methods required in v6.0 rc.1

[bokelley]

Closes #423

validate_platform() now surfaces the four sales-* methods that the spec promotes to required in v6.0 rc.1 — get_media_buys, provide_performance_feedback, list_creative_formats, list_creatives — as boot-time UserWarnings rather than silently tolerating their absence. A v3 ref seller would have shipped without them; this catches that class of gap at server boot.

What changed

src/adcp/decisioning/dispatch.py

• Added WARN_IF_MISSING_PER_SPECIALISM constant mapping all six sales-* specialisms to the four rc.1-promoted methods (private _SALES_WARN_IF_MISSING frozenset shared across all six entries)
• Added warning loop at the end of validate_platform(), after the governance gate, that emits one UserWarning per missing method — deduplicated across multi-specialism claims (e.g., a platform claiming both sales-non-guaranteed and sales-guaranteed warns once per method, not twice)
• Warning message names the concrete platform subclass via type(platform).__qualname__ so CI logs point at the adopter's file, and describes the consequence (AdcpError(NOT_SUPPORTED) at buyer call time)
• Updated stale inline comment in REQUIRED_METHODS_PER_SPECIALISM to say "warn-if-absent" instead of "present-or-absent, not enforced here"

src/adcp/decisioning/specialisms/sales.py

• Module docstring: replaced "Optional methods present-or-absent" section with "Warn-if-absent methods (v6.0 alpha → hard-required in v6.0 rc.1)" and a separate "Specialism-only required methods (already hard-enforced)" section for sync_catalogs
• # ---- Optional (gated by specialism — present-or-absent) ---- inline comment updated to # ---- Warn-if-absent (required in v6.0 rc.1 — hard-enforced at rc.1) ----
• Per-method docstrings on all four warn-if-absent methods updated from "Required when claiming any sales-* specialism in v6.0 rc.1+" to "UserWarning at boot / hard-error in v6.0 rc.1"

tests/test_decisioning_dispatch.py

• _ValidPlatform fixture upgraded from 5 → 9 methods (adds the four warn-if-absent stubs) so the "happy path" fixture is fully compliant and emits no warnings
• 4 new tests: warns on missing rc.1 methods, no-warn when all present, dedup across dual-specialism claim, contract pin for the new constant

What tested

• pytest tests/test_decisioning_dispatch.py — 42 passed (38 original + 4 new), 0 failed
• pytest tests/test_decisioning_advertised_per_specialism.py — 9 passed, 0 failed
• ruff check src/adcp/decisioning/dispatch.py src/adcp/decisioning/specialisms/sales.py — all checks passed
• mypy src/adcp/decisioning/dispatch.py src/adcp/decisioning/specialisms/sales.py — no issues found

Pre-PR review

• code-reviewer: approved — no blockers; nit on stale inline comment in REQUIRED_METHODS_PER_SPECIALISM (fixed in second commit)
• dx-expert: approved after fixes — two blockers resolved: sync_catalogs moved out of warn-if-absent section, # ---- Optional ---- comment updated; nits on __qualname__ in message and __all__ (both fixed)

Migration path to v6.0 rc.1

When rc.1 ships: move the four methods from WARN_IF_MISSING_PER_SPECIALISM into REQUIRED_METHODS_PER_SPECIALISM and drop them from the warn dict. The existing hard-error path in validate_platform() takes over. No new code needed.

Triage-managed PR. This bot does not currently iterate on
review comments or PR conversation threads (only on the source
issue). To unblock:

• Push fixup commits directly: gh pr checkout <num> →
  fix → push.
• Or re-trigger: comment /triage execute on the source
  issue.

See adcp#3121
for context.

Session: https://claude.ai/code/session_01GovN4hXXs27SNeNbBeFRgg

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[bokelley]

Closing in favor of #445 — same issue (#423), broader implementation (proper dedup, regression guards, strict mode env var, 7 tests vs ).

[bokelley]

Acknowledged — #445 supersedes this. Nothing further from triage.

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[bokelley]

Understood — noted that #445 supersedes this PR. No further triage action on #434.

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