Add text to core types and document type modifier policy

Core types:
- Add `text` as a core type for unlimited-length text (TEXT in both MySQL
  and PostgreSQL)

Type modifiers policy:
- Document that SQL modifiers (NOT NULL, DEFAULT, PRIMARY KEY, UNIQUE,
  COMMENT) are not allowed - DataJoint has its own syntax
- Document that AUTO_INCREMENT is discouraged but allowed with native types
- UNSIGNED is allowed as part of type semantics

Co-authored-by: dimitri-yatsenko <dimitri@datajoint.com>

Author: claude

docs/src/design/tables/attributes.md

@@ -34,6 +34,7 @@ Use these portable, scientist-friendly types for cross-database compatibility.
 
 -  `char(n)`: fixed-length string of exactly *n* characters.
 -  `varchar(n)`: variable-length string up to *n* characters.
+-  `text`: unlimited-length text for long-form content (notes, descriptions, abstracts).
 -  `enum(...)`: one of several enumerated values, e.g., `enum("low", "medium", "high")`.
    Do not use enums in primary keys due to difficulty changing definitions.
 
@@ -65,9 +66,9 @@ for portable pipelines. Using native types will generate a warning.
 -  `tinyint`, `smallint`, `int`, `bigint` (with optional `unsigned`)
 -  `float`, `double`, `real`
 -  `tinyblob`, `blob`, `mediumblob`, `longblob`
--  `text`, `mediumtext`, `longtext`
+-  `tinytext`, `mediumtext`, `longtext` (size variants)
 -  `time`, `timestamp`, `year`
--  `mediumint`, `serial`
+-  `mediumint`, `serial`, `int auto_increment`
 
 See the [storage types spec](storage-types-spec.md) for complete mappings.
 
@@ -133,10 +134,9 @@ class Measurement(dj.Manual):
 
 ## Datatypes not (yet) supported
 
--  `binary`
--  `text`
--  `longtext`
--  `bit`
+-  `binary(n)` / `varbinary(n)` - use `bytes` instead
+-  `bit(n)` - use `int` types with bitwise operations
+-  `set(...)` - use `json` for multiple selections
 
 For additional information about these datatypes, see
 http://dev.mysql.com/doc/refman/5.6/en/data-types.html

docs/src/design/tables/storage-types-spec.md

@@ -18,7 +18,7 @@ This document defines a three-layer type architecture:
 │                 Core DataJoint Types (Layer 2)                     │
 │                                                                    │
 │  float32  float64  int64  uint64  int32  uint32  int16  uint16    │
-│  int8  uint8  bool  uuid  json  bytes  date  datetime             │
+│  int8  uint8  bool  uuid  json  bytes  date  datetime  text       │
 │  char(n)  varchar(n)  enum(...)  decimal(n,f)                      │
 ├───────────────────────────────────────────────────────────────────┤
 │               Native Database Types (Layer 1)                      │
@@ -74,6 +74,7 @@ MySQL and PostgreSQL backends. Users should prefer these over native database ty
 |-----------|-------------|-------|------------|
 | `char(n)` | Fixed-length | `CHAR(n)` | `CHAR(n)` |
 | `varchar(n)` | Variable-length | `VARCHAR(n)` | `VARCHAR(n)` |
+| `text` | Unlimited text | `TEXT` | `TEXT` |
 
 ### Boolean
 
@@ -118,10 +119,34 @@ for serialized Python objects.
 
 ### Native Passthrough Types
 
-Users may use native database types directly (e.g., `text`, `mediumint auto_increment`),
+Users may use native database types directly (e.g., `mediumint`, `tinyblob`),
 but these will generate a warning about non-standard usage. Native types are not recorded
 in field comments and may have portability issues across database backends.
 
+### Type Modifiers Policy
+
+DataJoint table definitions have their own syntax for constraints and metadata. SQL type
+modifiers are **not allowed** in type specifications because they conflict with DataJoint's
+declarative syntax:
+
+| Modifier | Status | DataJoint Alternative |
+|----------|--------|----------------------|
+| `NOT NULL` / `NULL` | ❌ Not allowed | Position above/below `---` determines nullability |
+| `DEFAULT value` | ❌ Not allowed | Use `= value` syntax after type |
+| `PRIMARY KEY` | ❌ Not allowed | Position above `---` line |
+| `UNIQUE` | ❌ Not allowed | Use DataJoint index syntax |
+| `COMMENT 'text'` | ❌ Not allowed | Use `# comment` syntax |
+| `AUTO_INCREMENT` | ⚠️ Discouraged | Allowed with native types only, generates warning |
+| `UNSIGNED` | ✅ Allowed | Part of type semantics (use `uint*` core types) |
+
+**Auto-increment policy:** DataJoint discourages `AUTO_INCREMENT` / `SERIAL` because:
+- Breaks reproducibility (IDs depend on insertion order)
+- Makes pipelines non-deterministic
+- Complicates data migration and replication
+- Primary keys should be meaningful, not arbitrary
+
+If required, use native types: `int auto_increment` or `serial` (with warning).
+
 ## AttributeTypes (Layer 3)
 
 AttributeTypes provide `encode()`/`decode()` semantics on top of core types. They are

src/datajoint/declare.py

@@ -42,6 +42,8 @@
     # String types (with parameters)
     "char": (r"char\s*\(\d+\)$", None),
     "varchar": (r"varchar\s*\(\d+\)$", None),
+    # Unlimited text
+    "text": (r"text$", None),
     # Enumeration
     "enum": (r"enum\s*\(.+\)$", None),
     # Fixed-point decimal