fix(migrate): rewrite generated_poc imports to adcp.types.domains, split-aware

MIGRATION_v3_to_v4.md

@@ -25,11 +25,23 @@ python -m adcp.migrate v3-to-v4 ./src --auto-apply
 python -m adcp.migrate v3-to-v4 ./src --json
 ```
 
-`--auto-apply` implies `--apply` and additionally rewrites the ~78% of findings
-that are mechanically safe: `from adcp.types.generated_poc.X import Symbol` lines
-where every symbol has a known public alias on `adcp.types`, and `Assets<N>` numbered
-classes that have a documented semantic alias (`Assets81 → VideoFormatAsset`, etc.).
-`flag_removed` findings always require human attention.
+`--apply` rewrites the nine `<Type>Asset` renames and every
+`adcp.types.generated_poc` import path to `adcp.types.domains`, where the
+generated tree lives from 9.0 under the same module stems (see
+[generated_poc brand split](#generated_poc-brand-split) for the one stem that
+did not move whole). `--auto-apply` implies `--apply` and additionally rewrites
+the findings that are mechanically safe: `from adcp.types.generated_poc.X import
+Symbol` lines where every symbol has a known public alias on `adcp.types` are
+imported from there instead of the domain path, and `Assets<N>` numbered classes
+that have a documented semantic alias (`Assets81 → VideoFormatAsset`, etc.) are
+renamed. `flag_removed` findings always require human attention.
+
+Since the `generated_poc` → `domains` rename landed (#1417), a dry run whose only
+findings are deprecated `generated_poc` import paths exits 0: those are mechanical
+`rename_import` entries under `applied`, no longer `flag_private` entries. A CI
+drift gate that relied on the exit code to catch them should read `--json` and
+fail on a non-empty `applied` list (or simply run `--apply` in CI and fail on a
+dirty tree).
 
 The CLI exits 0 when all remaining findings are mechanical (or none); exits 1 when
 `flag_removed` findings remain for human review — wire it into CI to gate merges
@@ -78,10 +90,10 @@ felt blast radius, work in this order:
    re-export to the rest of your codebase (e.g. a `_base.py` schema barrel).
    Fix those before anything else — most of your test-collection failures
    disappear.
-2. **`adcp.types.generated_poc` reach-ins.** The codemod's per-symbol mapping
-   tells you the public alias for each (`ContextObject` →
-   `adcp.types.ContextObject`, etc.). Mechanical lookup once you know the
-   pattern.
+2. **`adcp.types.generated_poc` reach-ins.** `--apply` renames the path to
+   `adcp.types.domains`, and the report's hint names the public alias where a
+   symbol has one (`ContextObject` → `adcp.types.ContextObject`, etc.) so
+   `--auto-apply` can import it from the flat surface instead.
 3. **Numbered `Assets<N>` imports.** Switch to the semantic alias from
    `adcp.types`. See [Numbered discriminated-union classes
    shifted](#numbered-discriminated-union-classes-shifted) below.
@@ -317,6 +329,19 @@ result = await registry.lookup_brand("nike.com")
 manifest = result.brand  # Only `.brand`
 ```
 
+## generated_poc brand split
+
+`brand.json` shares its basename with the `brand/*.json` task schemas, so the
+pre-9.0 `adcp.types.generated_poc.brand` module *was* that discovery schema
+(`Brand`, `LocalizedName`, 138 more), while `adcp.types.domains.brand` is the
+aggregator over `domains/brand/<schema>.py`. The discovery classes are at
+`adcp.types.domains.brand_discovery`. `adcp migrate v3-to-v4 --apply` resolves
+each imported name to its half — a line that mixes the two becomes two import
+statements — and flags what it cannot place: a bare module reference such as
+`import adcp.types.generated_poc.brand as b` or a name neither half binds.
+Rewrite those by hand with the two module paths above. The deprecated name
+keeps serving both halves through 9.x; see `docs/types-9-migration.md`.
+
 ## Numbered discriminated-union classes shifted
 
 `datamodel-code-generator` numbers variant classes in the order they appear in

docs/types-9-migration.md

@@ -226,7 +226,9 @@ deleted and the generated models go back to agreeing with their schema.
   +from adcp.types.domains.media_buy.package_request import PackageRequest
   ```
 
-  `adcp migrate v3-to-v4` rewrites those lines. The old path also still
+  `adcp migrate v3-to-v4 --apply` rewrites those lines, and `--auto-apply`
+  additionally imports a name from `adcp.types` when every name on the line is
+  bound there. The old path also still
   resolves through the whole 9.x line, emitting a `DeprecationWarning` that
   names the new one — #1360 measured 110 such imports in a single production
   seller, and 9.0 does not break all of them at once. **It is removed in
@@ -250,6 +252,9 @@ deleted and the generated models go back to agreeing with their schema.
   +from adcp.types.domains.brand_discovery import Brand, LocalizedName
   ```
 
+  The codemod resolves this split per imported name — a line that mixes the
+  two halves becomes two import statements — and flags a bare
+  `adcp.types.generated_poc.brand` module reference it cannot place.
   The deprecated name keeps serving both halves for the 9.x line, so an
   unmigrated `from adcp.types.generated_poc.brand import Brand` still works and
   still returns the canonical class. It is the one deprecated name that is a

src/adcp/migrate/__main__.py

@@ -23,8 +23,9 @@ def main() -> int:
             "usage: python -m adcp.migrate <migration> <path> [options]\n"
             "\n"
             "Migrations:\n"
-            "  v3-to-v4    Rewrite <Type>Asset → <Type>Content and flag\n"
-            "              removed-type usages (BrandManifest, DeliverTo, etc).\n"
+            "  v3-to-v4    Rewrite <Type>Asset → <Type>Content, rename\n"
+            "              adcp.types.generated_poc imports to adcp.types.domains,\n"
+            "              and flag removed-type usages (BrandManifest, DeliverTo, etc).\n"
             "\n"
             "Run `python -m adcp.migrate <migration> --help` for per-migration options.\n",
             file=sys.stderr,