refactor: drop chat_model_configs provider column (#26877)

The provider type already lives authoritatively in ai_providers.type,
reachable on every active row through ai_provider_id, which the
chat_model_configs_ai_provider_required_when_active CHECK makes
mandatory. The stored provider string was a denormalized copy the system
kept in sync with a startup backfill and no longer needs.

Every surface now derives provider type from the linked ai_providers
row. Telemetry is the one exception: it keeps emitting provider, now
sourced from ai_providers.type via a JOIN, so the BigQuery column and the
Nexus dashboards that read it are unaffected. The experimental HTTP/SDK
response drops provider and makes ai_provider_id required, since those
endpoints return only active configs; consumers resolve provider type
from ai_provider_id and the AI providers listing.

This ships in a single release with no compatibility window: production
reads the table via SELECT *, so a pre-drop binary fails config reads the
moment the column is gone. Operators must scale to zero before upgrading,
and there is no rollback.

Closes CODAGT-599

coderd/database/queries/chatmodelconfigs.sql

@@ -18,20 +18,23 @@ WHERE
 
 -- name: GetChatModelConfigs :many
 SELECT
-    *
+    cmc.*
 FROM
-    chat_model_configs
+    chat_model_configs cmc
+LEFT JOIN
+    ai_providers ap ON ap.id = cmc.ai_provider_id
 WHERE
-    deleted = FALSE
+    cmc.deleted = FALSE
 ORDER BY
-    provider ASC,
-    model ASC,
-    updated_at DESC,
-    id DESC;
+    ap.type::text ASC,
+    cmc.model ASC,
+    cmc.updated_at DESC,
+    cmc.id DESC;
 
 -- name: GetEnabledChatModelConfigs :many
 SELECT
-    cmc.*
+    sqlc.embed(cmc),
+    ap.type::text AS provider
 FROM
     chat_model_configs cmc
 JOIN
@@ -42,7 +45,7 @@ WHERE
     AND ap.enabled = TRUE
     AND ap.deleted = FALSE
 ORDER BY
-    cmc.provider ASC,
+    ap.type::text ASC,
     cmc.model ASC,
     cmc.updated_at DESC,
     cmc.id DESC;
@@ -65,7 +68,6 @@ WHERE
 
 -- name: InsertChatModelConfig :one
 INSERT INTO chat_model_configs (
-    provider,
     model,
     display_name,
     created_by,
@@ -77,7 +79,6 @@ INSERT INTO chat_model_configs (
     options,
     ai_provider_id
 ) VALUES (
-    @provider::text,
     @model::text,
     @display_name::text,
     sqlc.narg('created_by')::uuid,
@@ -96,7 +97,6 @@ RETURNING
 UPDATE
     chat_model_configs
 SET
-    provider = @provider::text,
     model = @model::text,
     display_name = @display_name::text,
     updated_by = sqlc.narg('updated_by')::uuid,
@@ -133,38 +133,6 @@ SET
 WHERE
     id = @id::uuid;
 
--- name: DeleteChatModelConfigsByProvider :exec
-UPDATE
-    chat_model_configs
-SET
-    deleted = TRUE,
-    deleted_at = NOW(),
-    updated_at = NOW()
-WHERE
-    provider = @provider::text
-    AND deleted = FALSE;
-
--- name: BackfillChatModelConfigProvider :execresult
--- old_provider is matched as text; new_provider is also cast to ai_provider_type
--- for the EXISTS check against ai_providers.type.
--- ai_provider_id IS NOT NULL is defensive; the check constraint already
--- enforces that non-deleted rows always have a provider ID.
-UPDATE
-    chat_model_configs
-SET
-    provider   = @new_provider::text,
-    updated_at = NOW()
-WHERE
-    provider          = @old_provider::text
-    AND deleted       = FALSE
-    AND ai_provider_id IS NOT NULL
-    AND EXISTS (
-        SELECT 1 FROM ai_providers
-        WHERE  id      = chat_model_configs.ai_provider_id
-          AND  type    = @new_provider::ai_provider_type
-          AND  deleted = FALSE
-    );
-
 -- name: DeleteChatModelConfigsByAIProviderID :exec
 UPDATE
     chat_model_configs