dasSQLITE chunk 14b: typed ALTER macros + module rename

[borisbat]

Two commits, in order:

1. dasSQLITE: rename daslib/sql_migrate -> daslib/sqlite_migrate

Migrations as currently designed are SQLite-specific (the __schema_version audit table, BEGIN IMMEDIATE, unixepoch(), busy-timeout-based concurrent-runner contract). Sitting under the daslib/sql_* namespace would lie about provider neutrality. When the dasSQL abstraction lands, an abstract migration runner naturally takes the daslib/sql_migrate name; this provider-specific piece moves to daslib/sqlite_migrate. Doing the rename now keeps the public surface honest and avoids a churn migration when the abstraction lands.

Mechanical search-replace across 40 sites: file move + module sql_migrate -> module sqlite_migrate, internal qmacro sql_migrate::_add_migration_entry -> sqlite_migrate::, internal init thunk register'sql'migrations -> register'sqlite'migrations, all 23 test-side require sqlite/sql_migrate -> require sqlite/sqlite_migrate, mockup daslib/sql_migrate -> daslib/sqlite_migrate, prose references in API_REWORK / API_MIGRATION / API_MISSING / TUTORIALS / tutorials/sql/{39,41,42}-*.das + matching RST files, modules/dasSQLITE/.das_module sqlite_paths array, tests/aot/CMakeLists.txt AOT module list.

The annotation [sql_migration] is unchanged (SQL-level conceptual noun; an abstract migration layer landing later could reuse it).

2. dasSQLITE chunk 14b: typed ALTER macros

Adds the typed-ALTER ergonomics layer designed in API_MIGRATION.md Scenario 2 on top of the 14a migrations spine. New macros under daslib/sqlite_boost (transitively visible via daslib/sqlite_migrate's existing public re-export):

db |> add_column(type<T>, "Field" [, defaultLit])
db |> create_index(type<T>, "Field" | ("A","B") [, "name"])
db |> create_unique_index(type<T>, ... same shape ...)
db |> drop_index_if_exists("name")

What the macros buy:

• compile-time field-name + struct-shape checks (no more "user's DB panics on startup" surprises),
• type-derived NOT NULL: macro refuses to ADD a non-nullable column without a literal default; Option<T> wrapping = nullable,
• @sql_column rename + @sql_json / @sql_blob storage are honored, same conventions [sql_table] / [sql_index] already use,
• compile-time rejection for shapes that need a table rebuild (PK / UNIQUE inline / generated columns / @sql_default_fn).

Field selectors are string literals, not the .Field syntax used inside _sql {...} blocks — gen2's parser only synthesizes _ as a placeholder inside that block scope. Plain call sites pass explicit string field names, same convention [sql_index(fields="A")] already uses.

create_unique_index is a separate macro rather than a unique=true named arg because gen2's named-arg form [name=val] produces an ExprNamedCall that [call_macro] doesn't intercept; positional separation is cleaner.

Implementation notes:

• AddColumnMacro emits qmacro(_::exec($e(db), build_string $(w) { ... })) writing prefix + sql_storage_type_for(type<T>) + suffix — runtime SQL-type derivation via the existing _::sql_bind adapter rail.
• CreateIndex(Unique)Macro: pure macro-time DDL build via derive_index_name (extracted from SqlIndexMacro for reuse).
• drop_index_if_exists: 5-line runtime function, IF EXISTS native.
• is_option_field_type relaxed: now matches both the typeMacro pre-instantiation form (what [sql_table] sees during structure_macro apply()) AND the post-template-instantiation tStructure form (what call_macros see at infer time). The latter has _module=<callee> (downstream of the template instantiation site), so module-name matching was unsound — switched to "Option<...>" name-shape match.

Tests

16 new under tests/dasSQLITE/:

• 8 positives (migrate_14_* through migrate_21_*): Option<T> -> nullable; int + default=0 -> NOT NULL DEFAULT + backfill; embedded single-quote escaping in DEFAULT; @sql_column rename propagation; @sql_json -> TEXT; @sql_blob struct -> BLOB; auto-named single-col index; UNIQUE composite + named index + drop_index_if_exists idempotence.
• 1 runtime-error positive (migrate_22_add_column_dup_runtime): re-adding the same column at runtime panics inside the migration; α-shape transaction rolls back the whole call (audit table empty, table doesn't exist).
• 7 failed_* compile-error negatives: unknown field, no [sql_table], PK rejected, UNIQUE rejected, non-literal default, unknown index field, empty fields list.

tests/dasSQLITE: 748/748 pass interpreted and AOT, no GC leaks, lint clean, Sphinx clean (no warnings or errors).

Tutorial

tutorials/sql/43-migrations.das + doc/source/reference/tutorials/sql_43_migrations.rst refreshed:

• migrations 002 / 003 rewritten to use the typed forms (raw-SQL equivalent kept as a sidebar comment),
• new "Typed ALTER: when daslang has enough info to validate" section between Inspection and Adoption,
• migrations 004 / 005 added showing create_index + idempotent rebuild via drop_index_if_exists.

API_MIGRATION.md, API_REWORK.md, TUTORIALS.md updated to mark 14b as shipped. Chunk 14c (struct rebuild) remains pending.

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