feat: remove native chat cost tracking in favor of AI Gateway cost data (#27330)

## Stack Context

This stack makes AI Gateway data and budgets the source of truth for AI
spend controls.

1. Re-back the per-chat cost endpoint with AI Gateway data (#27328,
merged).
2. Remove native chat usage limits (#27329, merged).
3. **This PR, now based on `main`:** remove native chat cost tracking
and its dedicated admin UI.

## Summary

Removes native per-message price calculation, model pricing fields, cost
persistence, aggregate cost queries, and admin cost API types. It also
deletes the Analytics and Spend pages plus their legacy redirects. The
AI Gateway-backed per-chat cost row and compact budget indicators
remain.

The spend documentation is renamed to `spend-management.md` and updated
for the remaining surfaces, group budget APIs, CSV export, upgrade
handling for native pricing and cost history, and the absence of a
deployment-wide spend dashboard. The per-chat cost API documents that
data follows AI Gateway retention and reports zero after all matching
requests are purged.

No schema is dropped in this release. `chat_messages.total_cost_micros`
remains nullable and unwritten so replicas from the previous release can
continue inserting messages during rolling upgrades. #27600 tracks
removal after the compatibility window.

> Mux prepared this PR on Mike's behalf.

coderd/database/queries/chats.sql

@@ -941,7 +941,6 @@ inserted AS (
         cache_read_tokens,
         context_limit,
         compressed,
-        total_cost_micros,
         runtime_ms
     )
     SELECT
@@ -962,7 +961,6 @@ inserted AS (
         NULLIF((@cache_read_tokens::bigint[])[allocated.ord], 0),
         NULLIF((@context_limit::bigint[])[allocated.ord], 0),
         (@compressed::boolean[])[allocated.ord],
-        NULLIF((@total_cost_micros::bigint[])[allocated.ord], 0),
         NULLIF((@runtime_ms::bigint[])[allocated.ord], 0)
     FROM allocated
     RETURNING *
@@ -2211,229 +2209,6 @@ SELECT
     COUNT(*) FILTER (WHERE pull_request_state = 'closed')::bigint AS closed
 FROM deduped;
 
--- name: GetChatCostSummary :one
--- Aggregate cost summary for a single user within a date range.
--- Only counts assistant-role messages.
-SELECT
-    COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
-    COUNT(*) FILTER (
-        WHERE cm.total_cost_micros IS NOT NULL
-    )::bigint AS priced_message_count,
-    COUNT(*) FILTER (
-        WHERE cm.total_cost_micros IS NULL
-            AND (
-                cm.input_tokens IS NOT NULL
-                OR cm.output_tokens IS NOT NULL
-                OR cm.reasoning_tokens IS NOT NULL
-                OR cm.cache_creation_tokens IS NOT NULL
-                OR cm.cache_read_tokens IS NOT NULL
-            )
-    )::bigint AS unpriced_messages_having_usage_count,
-    COALESCE(SUM(cm.input_tokens), 0)::bigint AS total_input_tokens,
-    COALESCE(SUM(cm.output_tokens), 0)::bigint AS total_output_tokens,
-    COALESCE(SUM(cm.cache_read_tokens), 0)::bigint AS total_cache_read_tokens,
-    COALESCE(SUM(cm.cache_creation_tokens), 0)::bigint AS total_cache_creation_tokens,
-    COALESCE(SUM(cm.runtime_ms), 0)::bigint AS total_runtime_ms
-FROM
-    chat_messages cm
-JOIN
-    chats c ON c.id = cm.chat_id
-WHERE
-    c.owner_id = @owner_id::uuid
-    AND cm.role = 'assistant'
-    AND cm.created_at >= @start_date::timestamptz
-    AND cm.created_at < @end_date::timestamptz;
-
--- name: GetChatCostPerModel :many
--- Per-model cost breakdown for a single user within a date range.
--- Only counts assistant-role messages that have a model_config_id.
-SELECT
-    cmc.id AS model_config_id,
-    cmc.display_name,
-    COALESCE(ap.type::text, '')::text AS provider,
-    cmc.model,
-    COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
-    COUNT(*) FILTER (
-        WHERE cm.input_tokens IS NOT NULL
-            OR cm.output_tokens IS NOT NULL
-            OR cm.reasoning_tokens IS NOT NULL
-            OR cm.cache_creation_tokens IS NOT NULL
-            OR cm.cache_read_tokens IS NOT NULL
-    )::bigint AS message_count,
-    COALESCE(SUM(cm.input_tokens), 0)::bigint AS total_input_tokens,
-    COALESCE(SUM(cm.output_tokens), 0)::bigint AS total_output_tokens,
-    COALESCE(SUM(cm.cache_read_tokens), 0)::bigint AS total_cache_read_tokens,
-    COALESCE(SUM(cm.cache_creation_tokens), 0)::bigint AS total_cache_creation_tokens,
-    COALESCE(SUM(cm.runtime_ms), 0)::bigint AS total_runtime_ms
-FROM
-    chat_messages cm
-JOIN
-    chats c ON c.id = cm.chat_id
-JOIN
-    chat_model_configs cmc ON cmc.id = cm.model_config_id
-LEFT JOIN
-    ai_providers ap ON ap.id = cmc.ai_provider_id
-WHERE
-    c.owner_id = @owner_id::uuid
-    AND cm.role = 'assistant'
-    AND cm.created_at >= @start_date::timestamptz
-    AND cm.created_at < @end_date::timestamptz
-GROUP BY
-    cmc.id, cmc.display_name, ap.type, cmc.model
-ORDER BY
-    total_cost_micros DESC;
-
--- name: GetChatCostPerChat :many
--- Per-root-chat cost breakdown for a single user within a date range.
--- Groups by root_chat_id so forked chats roll up under their root.
--- Only counts assistant-role messages.
-WITH chat_costs AS (
-    SELECT
-        COALESCE(c.root_chat_id, c.id) AS root_chat_id,
-        COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
-        COUNT(*) FILTER (
-            WHERE cm.input_tokens IS NOT NULL
-                OR cm.output_tokens IS NOT NULL
-                OR cm.reasoning_tokens IS NOT NULL
-                OR cm.cache_creation_tokens IS NOT NULL
-                OR cm.cache_read_tokens IS NOT NULL
-        )::bigint AS message_count,
-        COALESCE(SUM(cm.input_tokens), 0)::bigint AS total_input_tokens,
-        COALESCE(SUM(cm.output_tokens), 0)::bigint AS total_output_tokens,
-        COALESCE(SUM(cm.cache_read_tokens), 0)::bigint AS total_cache_read_tokens,
-        COALESCE(SUM(cm.cache_creation_tokens), 0)::bigint AS total_cache_creation_tokens,
-        COALESCE(SUM(cm.runtime_ms), 0)::bigint AS total_runtime_ms
-    FROM chat_messages cm
-    JOIN chats c ON c.id = cm.chat_id
-    WHERE c.owner_id = @owner_id::uuid
-      AND cm.role = 'assistant'
-      AND cm.created_at >= @start_date::timestamptz
-      AND cm.created_at < @end_date::timestamptz
-    GROUP BY COALESCE(c.root_chat_id, c.id)
-)
-SELECT
-    cc.root_chat_id,
-    COALESCE(rc.title, '') AS chat_title,
-    cc.total_cost_micros,
-    cc.message_count,
-    cc.total_input_tokens,
-    cc.total_output_tokens,
-    cc.total_cache_read_tokens,
-    cc.total_cache_creation_tokens,
-    cc.total_runtime_ms
-FROM chat_costs cc
-LEFT JOIN chats rc ON rc.id = cc.root_chat_id
-ORDER BY cc.total_cost_micros DESC;
-
--- name: GetChatModelUsageCostByChatID :one
--- Assistant-message cost rolled up over the requested chat's subtree: the
--- chat itself plus every descendant reachable through parent_chat_id. A
--- root chat therefore reports its whole tree, while a subagent chat
--- reports only its own spend plus any nested subagents it spawned.
-WITH RECURSIVE target AS (
-    SELECT @chat_id::uuid AS chat_id
-), subtree AS (
-    SELECT chat_id AS id FROM target
-    UNION ALL
-    SELECT c.id
-    FROM chats c
-    JOIN subtree s ON c.parent_chat_id = s.id
-), costs AS (
-    SELECT
-        COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
-        COUNT(*) FILTER (
-            WHERE cm.total_cost_micros IS NOT NULL
-        )::bigint AS priced_message_count,
-        COUNT(*) FILTER (
-            WHERE cm.total_cost_micros IS NULL
-                AND (
-                    cm.input_tokens IS NOT NULL
-                    OR cm.output_tokens IS NOT NULL
-                    OR cm.reasoning_tokens IS NOT NULL
-                    OR cm.cache_creation_tokens IS NOT NULL
-                    OR cm.cache_read_tokens IS NOT NULL
-                )
-        )::bigint AS unpriced_messages_having_usage_count
-    FROM chat_messages cm
-    JOIN subtree s ON s.id = cm.chat_id
-    WHERE cm.role = 'assistant'
-)
-SELECT
-    t.chat_id,
-    costs.total_cost_micros,
-    costs.priced_message_count,
-    costs.unpriced_messages_having_usage_count
-FROM target t
-CROSS JOIN costs;
-
--- name: GetChatCostPerUser :many
--- Deployment-wide per-user cost rollup within a date range.
--- Only counts assistant-role messages.
-WITH chat_cost_users AS (
-    SELECT
-        c.owner_id AS user_id,
-        u.username,
-        u.name,
-        u.avatar_url,
-        COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
-        COUNT(*) FILTER (
-            WHERE cm.input_tokens IS NOT NULL
-                OR cm.output_tokens IS NOT NULL
-                OR cm.reasoning_tokens IS NOT NULL
-                OR cm.cache_creation_tokens IS NOT NULL
-                OR cm.cache_read_tokens IS NOT NULL
-        )::bigint AS message_count,
-        COUNT(DISTINCT COALESCE(c.root_chat_id, c.id))::bigint AS chat_count,
-        COALESCE(SUM(cm.input_tokens), 0)::bigint AS total_input_tokens,
-        COALESCE(SUM(cm.output_tokens), 0)::bigint AS total_output_tokens,
-        COALESCE(SUM(cm.cache_read_tokens), 0)::bigint AS total_cache_read_tokens,
-        COALESCE(SUM(cm.cache_creation_tokens), 0)::bigint AS total_cache_creation_tokens,
-        COALESCE(SUM(cm.runtime_ms), 0)::bigint AS total_runtime_ms
-    FROM
-        chat_messages cm
-    JOIN
-        chats c ON c.id = cm.chat_id
-    JOIN
-        users u ON u.id = c.owner_id
-    WHERE
-        cm.role = 'assistant'
-        AND cm.created_at >= @start_date::timestamptz
-        AND cm.created_at < @end_date::timestamptz
-        AND (
-            @username::text = ''
-            OR u.username ILIKE '%' || @username::text || '%'
-            OR u.name ILIKE '%' || @username::text || '%'
-        )
-    GROUP BY
-        c.owner_id,
-        u.username,
-        u.name,
-        u.avatar_url
-)
-SELECT
-    user_id,
-    username,
-    name,
-    avatar_url,
-    total_cost_micros,
-    message_count,
-    chat_count,
-    total_input_tokens,
-    total_output_tokens,
-    total_cache_read_tokens,
-    total_cache_creation_tokens,
-    total_runtime_ms,
-    COUNT(*) OVER()::bigint AS total_count
-FROM
-    chat_cost_users
-ORDER BY
-    total_cost_micros DESC,
-    username ASC
-LIMIT
-    sqlc.arg('page_limit')::int
-OFFSET
-    sqlc.arg('page_offset')::int;
-
 -- name: GetTotalChatMessageRuntimeMsInRange :one
 -- Computes hb_agent_runtime_v1 usage event payloads. Deliberately includes
 -- soft-deleted messages and messages from all chats.
@@ -2443,22 +2218,6 @@ WHERE cm.created_at >= @start_time::timestamptz
   AND cm.created_at < @end_time::timestamptz
   AND cm.runtime_ms IS NOT NULL;
 
--- name: CountEnabledModelsWithoutPricing :one
--- Counts enabled, non-deleted model configs that lack both input and
--- output pricing in their JSONB options.cost configuration.
-SELECT COUNT(*)::bigint AS count
-FROM chat_model_configs
-WHERE enabled = TRUE
-  AND deleted = FALSE
-  AND (
-    options->'cost' IS NULL
-    OR options->'cost' = 'null'::jsonb
-    OR (
-      (options->'cost'->>'input_price_per_million_tokens' IS NULL)
-      AND (options->'cost'->>'output_price_per_million_tokens' IS NULL)
-    )
-  );
-
 -- name: GetChatsByWorkspaceIDs :many
 SELECT *
 FROM chats_expanded
@@ -2521,7 +2280,6 @@ SELECT
     COALESCE(SUM(cm.reasoning_tokens), 0)::bigint AS total_reasoning_tokens,
     COALESCE(SUM(cm.cache_creation_tokens), 0)::bigint AS total_cache_creation_tokens,
     COALESCE(SUM(cm.cache_read_tokens), 0)::bigint AS total_cache_read_tokens,
-    COALESCE(SUM(cm.total_cost_micros), 0)::bigint AS total_cost_micros,
     COALESCE(SUM(cm.runtime_ms), 0)::bigint AS total_runtime_ms,
     COUNT(DISTINCT cm.model_config_id)::bigint AS distinct_model_count,
     COUNT(*) FILTER (WHERE cm.compressed)::bigint AS compressed_message_count