Closes #559.

The bug

`@IdempotencyStore.wrap` had signature `(handler_self, params, context=None, *args, **kwargs)`. The framework's arg-projector path in `dispatch.py:1081` calls methods as `method(**arg_projector, ctx=ctx)` — for `update_media_buy`, that's `method(self, media_buy_id=..., patch=..., ctx=...)`. Python can't bind `params` (positional, no default) → `TypeError: missing 1 required positional argument: 'params'` before the wrap body runs.

Salesagent's kill-nginx spike shipped a workaround dropping `@_IDEMPOTENCY.wrap` from `update_media_buy` entirely. Buyer retries re-execute side effects.

Fix

Wrap signature is now `async def _wrapped(*args, **kwargs)`. A new `_resolve_call_args` helper detects which of three calling conventions the framework dispatched with:

1. Positional: `(self, params, ctx)` — default for non-projected tools.
2. Keyword: `(self, params=..., context=...)`.
3. Arg-projected: `(self, **arg_projector_kwargs, ctx=...)` — searches kwargs for a Pydantic model (the framework's contract for the request model, e.g. `patch` on `update_media_buy`) and uses it as the hash source. Falls back to the kwargs dict (excluding `ctx` / `context`) when no Pydantic model is present.

The inner handler is invoked via `*args/**kwargs` verbatim. The wrap is signature-transparent — no matter which convention the framework used, the inner handler sees its expected arguments unchanged.

Why a wrap-side fix (not dispatch-side)?

Three reasons:

• Dispatch is generic and shouldn't know about `@wrap` — the abstraction was already correct.
• Adopters who call `@store.wrap` outside the framework dispatch (in custom transports, in tests) get the fix automatically without retrofitting their callers.
• The `_resolve_call_args` heuristic uses a public Pydantic contract (`hasattr(value, "model_dump")`), not framework-internal knowledge, so future arg-projector additions work without further wrap changes.

Edge cases handled

• `update_media_buy` (`arg_projector={"media_buy_id": id, "patch": }`): finds `patch` (the only Pydantic kwarg), extracts `idempotency_key` from it. Cache hit + replay + conflict all work. ✅
• `sync_audiences` style (`arg_projector={"audiences": [...]}`): no Pydantic model, no top-level `idempotency_key` → wrap finds no key, runs handler without dedup. Same fall-through as before for missing-key — not a regression. Adopters who want idempotency on this shape should project the request model directly. ✅
• Top-level `idempotency_key` in arg_projector kwargs: fallback path treats kwargs (minus `ctx`/`context`) as the hash source. Dedup works. ✅
• Cross-principal isolation: arg-projected calls use `ctx=` (not `context=`). The resolver checks both. Same key from different principals → different cache scope (no cross-principal replay). ✅
• Conflict on same key + different patch: `IdempotencyConflictError` raised, parity with positional path. ✅

Tests

6 new in `TestWrapArgProjectionCalling`:

• `update_media_buy` shape: cache hit, replay, conflict
• `sync_audiences` style: no-key fall-through
• Top-level `idempotency_key` fallback
• `ctx=` kwarg scope-key extraction (cross-principal isolation)
• Keyword convention (`params=`, `context=`)

154 tests green across the broader idempotency surface (validate-wiring, PG backend, MCP/A2A integration). Lint clean.

Test plan

• `pytest tests/test_server_idempotency.py` — 55 passed (49 existing + 6 new)
• `pytest tests/test_idempotency.py tests/test_validate_idempotency_wiring.py tests/test_pg_idempotency_backend.py` — 154 total green
• `ruff check` — clean
• Salesagent re-applies `@_IDEMPOTENCY.wrap` to `update_media_buy` and verifies storyboard runner passes

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