driver-sql: a PLAIN unique index (no organization key part) over existing duplicate rows fails the boot with the raw driver error naming no rows and no remedy, and `os migrate plan` classifies the same op `safe` with no duplicate pre-flight

[os-sam]

Measured while implementing #13894 (autonumber fields default to unique: 'organization'), on origin/main 2263ca4d6, sqlite (better-sqlite3). Filed unassigned for the engine lane — the #13894 dispatch fences packages/drivers/** as measurement-only (PR #14773 is open on sql-driver.ts).

The two shapes, side by side

Same fixture: table crm_quote with two rows sharing quote_number = 'QUO-00009', then initObjects with quote_number: { type: 'autonumber', unique: true }.

A — organization-scoped object (the NULL-safe composite path). The boot continues; the driver logs at error naming the index, the unenforced constraint and the remedy; the same boot's drift pass names the conflicting key groups with row counts; os migrate plan (detectManagedDrift) reports the blocked create_index (category: 'destructive', severity: 'error') with the same groups. This is the ADR-0120 D4 posture and it is the one #13894's default relies on. Verbatim:

[sql-driver] cannot create NULL-safe unique index 'uniq_crm_quote_organization_id_quote_number' on "crm_quote" — existing rows violate it (duplicates the previous NULL-distinct index admitted, #5030). The constraint 'organization_id, quote_number' is NOT enforced until the data is deduplicated: run "os migrate plan" for the conflicting rows (ADR-0120 D4).
[schema-drift] crm_quote: cannot create 'uniq_crm_quote_organization_id_quote_number' as UNIQUE (COALESCE(organization_id, '__global__'), quote_number) — existing rows already violate the NULL-safe unique constraint (duplicates the old index wrongly admitted, #5030): (organization_id="__global__", quote_number="QUO-00009") × 2 rows; (organization_id="org_x", quote_number="QUO-00010") × 2 rows. The op is BLOCKED: apply re-probes and refuses, and the existing index stays in place (ADR-0120 D4). Deduplicate the listed rows, then re-run "os migrate plan".

B — tenancy: { enabled: false } (the plain single-column path). initObjects THROWS the database's own error — the boot dies, the message names the index/column but no rows and no remedy, nothing is logged on the durability channel:

create unique index `uniq_crm_quote_quote_number` on `crm_quote` (`quote_number`) - UNIQUE constraint failed: crm_quote.quote_number   (code=SQLITE_CONSTRAINT_UNIQUE)

and detectManagedDrift() for the same table reports the op as harmless:

{ kind: 'index_mismatch', expected: 'UNIQUE (quote_number)', actual: '(absent)', severity: 'warning', category: 'safe',
  message: "crm_quote: metadata declares index 'uniq_crm_quote_quote_number' UNIQUE (quote_number) but the database has no such index — run \"os migrate apply\" to create it." }

so os migrate apply (and dev autoMigrate: 'safe') would walk into the same raw failure with no pre-flight.

Where in the code

• packages/drivers/driver-sql/src/sql-driver.ts syncDeclaredIndexes: the catch absorbs a unique violation only when nullSafe.size > 0 (isUniqueViolationError(e) → logDurabilityFailure + continue); the plain path falls through to throw e.
• applyNullSafeUniquePreflight (ADR-0120 D4) probes only ops carrying nullSafeColumns, so a plain unique create_index keeps its default safe category and never gets a row report.

Why it matters more after #13894

The default flip makes every autonumber field unique. On an organization-scoped object that lands on path A (loud, non-fatal, rows named). On an object that opted out of tenancy — or on any plain unique: 'global' field — it lands on path B: a table with legacy duplicates takes the whole boot down with a message an operator cannot act on, and the plan that should have warned them says safe.

Suggested shape (engine lane's call)

Extend the D4 pre-flight to plain unique create_index ops (GROUP BY the bare columns HAVING COUNT(*) > 1 — probeNullSafeUniqueDuplicates already handles a column list with an empty NULL-safe set), and give the sync's catch the same "log at error naming the constraint and the remedy, then continue" posture for a unique violation on the plain path, so both paths are loud and neither is fatal or silent. os migrate duplicates (#8928) deliberately reports only cross-partition duplicates and is not the channel for this.

Refs: #13894, #5030, ADR-0120 D4, #8928.