Add many-to-many include support via a single correlated subquery that
joins the child table to the junction on junction.childColumns = child.targetColumns
and correlates to the parent via WHERE junction.parentColumns = parent.parentLocalColumns.
Composite keys AND across all column pairs. No LATERAL joins.

- IncludeExpr gains `through?: IncludeThroughDescriptor` carrying junction table
  name, parentColumns, childColumns, targetColumns, and parentLocalColumns.
- `resolveIncludeRelation` in collection-contract.ts surfaces `through` from the
  contract relation when present, resolving field names to column names for the
  parent local columns.
- `Collection.include()` propagates `through` into IncludeExpr via spread.
- `buildManyToManyJunctionArtifacts` in query-plan-select.ts builds the JOIN ON
  expression (BinaryExpr or AndExpr over child column pairs) and the correlated
  WHERE (BinaryExpr or AndExpr over parent column pairs), producing a non-lateral
  inner JoinAst to the junction table.
- `buildIncludeChildRowsSelect` detects `include.through` and uses the M:N
  artifacts instead of the FK equality WHERE; `buildDistinctNonLeafChildRowsSelect`
  receives and applies the same junction joins.
- `dispatchWithIncludes` in collection-dispatch.ts forces all `through.parentLocalColumns`
  (not just `localColumn`) into the parent SELECT augmentation for composite M:N keys.
- `buildManyToManyContract` test helper and M:N unit tests covering single-column
  and composite-key junction shapes, plus a FK path non-regression test.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

…ManyJunctionArtifacts; add M:N+distinct+non-leaf test

F1: the two bare `as AnyExpression` casts in `buildManyToManyJunctionArtifacts` are replaced with
`castAs<AnyExpression>(…!)` — BinaryExpr is a union member of AnyExpression, so the assertion is
type-checked; the non-null assertion is safe because the branch is only taken when `length === 1`.
Adds the `castAs` import from `@prisma-next/utils/casts`. `lint:casts` delta: -1.

F2: new unit test `attaches junction join to baseInner in M:N + distinct + nested non-leaf path`
in the `M:N include correlated subquery` describe block. Constructs a contract with
parents→children (M:N via parent_child junction) + children→grandchildren (FK), sets
`distinct: ['name']` and a nested grandchild include on the M:N IncludeExpr, calls
`compileSelectWithIncludes`, and asserts:
  - junction join (`INNER JOIN parent_child`, `lateral: false`) attaches to `baseInner`
    (the innermost scalar SELECT inside the ROW_NUMBER wrap), not to the dedup wrapper or
    outer distinct SELECT
  - correlated WHERE (`parent_child.parent_id = parents.id`) is present at `baseInner`
  - no junction join leaks to `innerSelect` or the outer `childRows`

All 493 tests pass; typecheck clean.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

Adds `mn-include.test.ts` covering the end-to-end M:N include path for
`User.tags` via the `user_tags` junction, using the PGlite harness.

Tests satisfy the operator integration-test standard:
- Whole-row toEqual assertions on every test
- Explicit .select() on 6/7 tests
- One implicit/default-selection test (full User + tags: Tag[] shape)
- Single-execution assertion + no LATERAL in emitted SQL
- Depth-2: M:N tags nested under invitedUsers (1:N self-relation)
- Sibling depth-2: include("tags") alongside include("posts") in one execution
- Edge: user with no tags returns tags: []
- Edge: tag shared by multiple users resolves independently for each

Also extends `setupTestSchema` and adds `seedTags`/`seedUserTags` helpers
to `runtime-helpers.ts` to support the junction table in integration tests.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

… (TML-2785)

Orchestrator artifacts for the read slice (fixture / read-path / integration
dispatches; read-path took 3 rounds incl. a truncation recovery). Review log
under reviews/ is gitignored.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

…-2605 rebase

Carry the resolved junction namespaceId onto IncludeThroughDescriptor and
build the correlated include's junction TableSource with it, so the read
path emits namespace-qualified SQL for the junction like the rest of the
runtime after TML-2605.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

…ough descriptor

The contract now carries the junction's namespaceId on through (slice 0);
the include descriptor passes it through as a required field instead of
re-deriving it from storage. Re-emit the M:N fixture so the User<->Tag
through block carries it.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

… M:N contracts (TML-2808 rebase)

Main moved namespace tables under entries.table; the hand-built M:N test
contracts still used the flat tables record, so table resolution missed
them.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

…eated_at)

The shared fixture's junction declares a nullable note and a defaulted
created_at (exclusion-path coverage for requiredPayloadColumns); create
the columns so the schema matches the contract.

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>