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+# Constructor PRE snapshots
+
+When argument dumping is enabled for a class's `__init__`, TrainCheck records
+the receiver before the initializer body runs. The receiver may be empty,
+partially initialized by a subclass, or being initialized again. The instrumenter
+identifies initializers from their owning class and attribute name; a standalone
+function named `__init__` keeps ordinary argument serialization.
+
+The receiver is encoded under its static, fully qualified type name with an
+`_TRAINCHECK_CONSTRUCTOR_SNAPSHOT` marker. This is a deliberate change from
+ordinary object introspection for **all selected initializers**, including
+metaclass initializers. Other arguments and ordinary method calls keep their
+existing representation. The function's PRE, POST, and exception records remain.
+
+## Stored-state contract
+
+The marker contains:
+
+| Field | Meaning |
+| --- | --- |
+| `phase` | `before_init`; this does not claim initialization succeeded. |
+| `coverage` | `stored_attributes_only`; computed properties are not captured. |
+| `object_id` | Identity of the actual receiver. |
+| `dictionary_status` | `captured`, `absent`, or `unavailable` when storage exists but no native accessor remains accessible. |
+| `attributes` | Selected entries from the instance dictionary or native class namespace. |
+| `slots` | Selected populated native slots, each with its declaring `owner_type`, `name`, and tagged `value`. |
+| `unset_slots` | Selected declared slots whose storage has not been assigned. |
+| `requested_attributes` | The explicit selector, or `null` for all accessible stored fields. |
+| `unavailable_attributes` | Requested names with no captured dictionary entry or populated slot. |
+
+Dictionary entries and slot records are separate. A base slot, a derived slot,
+and a dictionary entry can all have the same name and hold different values;
+none overwrites another. Slot selectors use the stored name, including Python's
+name mangling for private slots. A requested name selects each matching storage
+location. An unset location stays explicit even if another matching slot has a
+value. An empty selector is distinct from unselected/all-field collection.
+
+Exact built-in scalars retain their values. Nonfinite floats have explicit
+`nan`, `+inf`, and `-inf` tags. Other values, including containers and tensors,
+are **identity/type references**, not recursive content snapshots or tensor
+hashes. Missing storage is never represented as a stored `None` value.
+
+## Avoiding application execution
+
+The snapshot reads native dictionary and slot descriptors from raw class
+namespaces. It bypasses receiver `__getattribute__`, `__getattr__`, `__dir__`,
+properties, custom descriptors, and custom metaclass lookup/properties. It also
+bypasses overridden dictionary iteration methods and custom metaclass equality.
+Constructor receivers are excluded from proxy-marker scans and argument
+unproxying on this dumping path; ordinary arguments keep those behaviors.
+
+Normal positional construction and explicit keyword-receiver calls are covered.
+If a native callable exposes no signature, its positional receiver is supported;
+no keyword receiver name is guessed. Missing-receiver errors are produced by
+the original callable and retain an exception record.
+
+Native extension state without a recognized storage descriptor, replaced slot
+descriptors, and computed attributes are outside this snapshot's coverage.
+Dictionary storage hidden behind a replacement property is marked unavailable
+unless an inherited native accessor still exposes it. Snapshots are synchronous,
+do not cache application metadata, and do not promise an atomic view during
+concurrent mutation of the same object's storage.
+
+Existing invariants that depended on introspected constructor receiver fields
+need recollection and activation validation against this representation. A
+requested property is explicitly unavailable, not a successfully observed value.