Drop unused agent_messages.read_at column via migration v49 (M1)

The `agent_messages.read_at` column has had no production writer since
v12 moved read tracking into the per-viewer `agent_message_reads`
receipts table. It survived anyway, carrying a NULL through every SELECT
list and begging the next maintainer to accidentally read stale data
from it.

- v49 migration: `ALTER TABLE agent_messages DROP COLUMN read_at`
  (idempotent: skips if absent).
- messages.ts: SELECTs no longer fetch the column; per-viewer `readAt`
  is computed from `agent_message_reads` as before, with `null` for
  call-sites that have no viewer context (getAgentMessage /
  searchMessages / listAgentInboxUnread).
- runtime-bridge.ts / runtime-message-injector.ts: comments referencing
  the dropped column updated to name the read-receipts table instead.

src/main/database/messages.ts

@@ -107,10 +107,15 @@ export function buildMessageMethods(
     getAgentMessage(messageId: string, companyId: string): AgentMessageRecord | null {
       const row = getDb()
         .prepare(
-          "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, read_at as readAt, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages where id = ? and company_id = ?",
+          "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages where id = ? and company_id = ?",
         )
-        .get(messageId, companyId) as AgentMessageRecord | undefined;
-      return row ?? null;
+        .get(messageId, companyId) as Omit<AgentMessageRecord, "readAt"> | undefined;
+      if (!row) return null;
+      // `readAt` is a per-viewer computed field resolved from
+      // agent_message_reads at the callers that need it (inbox
+      // projection, renderer snapshot). This single-row lookup has no
+      // viewer context, so the field is surfaced as `null`.
+      return { ...row, readAt: null };
     },
 
     listAgentMessages(
@@ -125,8 +130,12 @@ export function buildMessageMethods(
       },
     ): AgentMessageRecord[] {
       const limit = opts?.limit ?? 200;
+      // `readAt` is resolved from `agent_message_reads` further down,
+      // per viewer (BOARD_READER_ID for the operator-wide path, the
+      // specific agent id for the per-agent path). The column lives
+      // outside the row itself since v49.
       const selectCols =
-        "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, read_at as readAt, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages";
+        "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages";
       let sql = `${selectCols} where company_id = ?`;
       const params: SQLInputValue[] = [companyId];
       if (opts?.messageId) {
@@ -148,7 +157,7 @@ export function buildMessageMethods(
           sql += " limit ?";
           params.push(limit);
         }
-        const rows = readAll<AgentMessageRecord>(sql, ...params).reverse();
+        const rows = readAll<Omit<AgentMessageRecord, "readAt">>(sql, ...params).reverse();
         const boardReadReceiptMap = new Map(
           readAll<{ messageId: string; readAt: string }>(
             `select reads.message_id as messageId, reads.read_at as readAt
@@ -219,7 +228,7 @@ export function buildMessageMethods(
         sql += " limit ?";
         params.push(limit);
       }
-      const rows = readAll<AgentMessageRecord>(sql, ...params).reverse();
+      const rows = readAll<Omit<AgentMessageRecord, "readAt">>(sql, ...params).reverse();
 
       const readReceiptMap = new Map(
         readAll<{ messageId: string; readAt: string }>(
@@ -260,7 +269,7 @@ export function buildMessageMethods(
       const pattern = `%${escaped}%`;
       let sql = `SELECT id, company_id AS companyId, from_agent_id AS fromAgentId,
       to_agent_id AS toAgentId, sender_kind AS senderKind, channel, channel_target_id AS channelTargetId,
-      subject, body, priority, read_at AS readAt, parent_message_id AS parentMessageId,
+      subject, body, priority, parent_message_id AS parentMessageId,
       attachments_json AS attachmentsJson, created_at AS createdAt
       FROM agent_messages WHERE company_id = ? AND (subject LIKE ? ESCAPE '\\' OR body LIKE ? ESCAPE '\\')`;
       const params: SQLInputValue[] = [companyId, pattern, pattern];
@@ -274,7 +283,11 @@ export function buildMessageMethods(
       }
       sql += " ORDER BY created_at DESC LIMIT ?";
       params.push(opts?.limit ?? 50);
-      return readAll<AgentMessageRecord>(sql, ...params);
+      // Operator-facing search has no viewer context — `readAt` is
+      // surfaced as `null`. Callers that need per-viewer read state
+      // pull it from `agent_message_reads` separately (inbox projection,
+      // snapshot).
+      return readAll<Omit<AgentMessageRecord, "readAt">>(sql, ...params).map((row) => ({ ...row, readAt: null }));
     },
 
     markMessageReadForReader(
@@ -301,12 +314,11 @@ export function buildMessageMethods(
      * department when agent belongs, project when assigned/lead).
      *
      * "Unread" is defined uniformly across every channel: no row in
-     * `agent_message_reads` for (message_id, agent_id). The legacy
-     * `agent_messages.read_at` column is never written anywhere in the
-     * codebase and must not be used as a read signal — it only appears in
-     * SELECT lists for wire-shape compatibility and is overwritten from the
-     * read-receipts table by every caller that surfaces `readAt` to agents
-     * or the renderer.
+     * `agent_message_reads` for (message_id, agent_id). The row's
+     * `readAt` field is always `null` here because callers want the
+     * unread set — per-viewer read state lives exclusively in the
+     * `agent_message_reads` join table since v49 dropped the redundant
+     * `agent_messages.read_at` column.
      *
      * Messages where `from_agent_id = agentId` are excluded (agents don't
      * inject their own sent messages back into their transcript).
@@ -362,9 +374,9 @@ export function buildMessageMethods(
       }
 
       const selectCols =
-        "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, read_at as readAt, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages";
+        "select id, company_id as companyId, from_agent_id as fromAgentId, to_agent_id as toAgentId, sender_kind as senderKind, channel, channel_target_id as channelTargetId, subject, body, priority, parent_message_id as parentMessageId, attachments_json as attachmentsJson, created_at as createdAt from agent_messages";
       const sql = `${selectCols} where company_id = ? and from_agent_id != ? and (${visibilityClauses.join(" or ")}) order by created_at asc`;
-      const rows = readAll<AgentMessageRecord>(sql, companyId, agentId, ...visibilityParams);
+      const rows = readAll<Omit<AgentMessageRecord, "readAt">>(sql, companyId, agentId, ...visibilityParams).map((row) => ({ ...row, readAt: null }));
 
       const readIds = new Set(
         readAll<{ messageId: string }>(

src/main/database/migrations/v49-v49.ts

@@ -0,0 +1,40 @@
+import log from "electron-log/main.js";
+import type { Migration, MigrationDeps } from "./types";
+import { columnExists, tableExists } from "./types";
+
+/**
+ * Drop the unused `agent_messages.read_at` column.
+ *
+ * The column was added in v11 when reads were tracked per-message on a
+ * single shared receipt. v12 moved read tracking to the
+ * `agent_message_reads` join table, which is now the sole source of
+ * truth: every consumer that surfaces `readAt` (renderer snapshot,
+ * per-agent inbox, board receipts) resolves it from that table.
+ * `agent_messages.read_at` has not been written by any production path
+ * for multiple releases; leaving it around just forced every SELECT to
+ * carry a NULL column through wire-shape layers and invited the next
+ * maintainer to accidentally read stale data from it.
+ */
+export function createMigrationsV49V49(deps: MigrationDeps): Migration[] {
+  const { db } = deps;
+  return [
+    {
+      version: 49,
+      name: "drop_agent_messages_read_at",
+      fn: () => {
+        if (!tableExists(db, "agent_messages")) {
+          log.info("[migration v49] agent_messages table missing; skipping");
+          return;
+        }
+        if (!columnExists(db, "agent_messages", "read_at")) {
+          log.info("[migration v49] agent_messages.read_at already absent; skipping");
+          return;
+        }
+        db.exec("ALTER TABLE agent_messages DROP COLUMN read_at");
+        log.info(
+          "[migration v49] dropped unused agent_messages.read_at column — reads are tracked per-reader in agent_message_reads",
+        );
+      },
+    },
+  ];
+}

src/main/database/schema.ts

@@ -14,6 +14,7 @@ import { createMigrationsV45V45 } from "./migrations/v45-v45";
 import { createMigrationsV46V46 } from "./migrations/v46-v46";
 import { createMigrationsV47V47 } from "./migrations/v47-v47";
 import { createMigrationsV48V48 } from "./migrations/v48-v48";
+import { createMigrationsV49V49 } from "./migrations/v49-v49";
 import {
   columnExists,
   nowIso,
@@ -208,6 +209,7 @@ export function runMigrations(
     ...createMigrationsV46V46(deps),
     ...createMigrationsV47V47(deps),
     ...createMigrationsV48V48(deps),
+    ...createMigrationsV49V49(deps),
   ];
 
   // Pre-migration snapshot. If any migration is pending we take a full

src/main/database/snapshot.ts

@@ -41,8 +41,9 @@ export function buildSnapshotMethods(
     // view has exactly one human viewer (the Board operator), so the
     // renderer snapshot fills it from that reader's agent_message_reads
     // rows. Agent-side queries (listAgentMessages) resolve it against
-    // the current agent's receipts. The raw agent_messages.read_at
-    // column is never read on any path and stays NULL by design.
+    // the current agent's receipts. The old `agent_messages.read_at`
+    // column was dropped in migration v49 — the join table is the
+    // sole source of truth.
     const boardReadReceiptMap = new Map(
       readAll<{ messageId: string; readAt: string }>(
         `select reads.message_id as messageId, reads.read_at as readAt
@@ -183,10 +184,9 @@ export function buildSnapshotMethods(
         createdAt: r.created_at, updatedAt: r.updated_at,
       })),
       agentMessages: readAll<SqliteRow>(
-        // The raw `read_at` column is intentionally omitted from the
-        // SELECT list. It is never written — readAt semantics live in
-        // the agent_message_reads receipts table, resolved against the
-        // current viewer above.
+        // readAt semantics live in the agent_message_reads receipts
+        // table, resolved against the current viewer above. The old
+        // `agent_messages.read_at` column was dropped in v49.
         `select id, company_id, from_agent_id, to_agent_id, sender_kind, channel, channel_target_id, subject, body, priority, parent_message_id, attachments_json, created_at from agent_messages${companyWhere} order by created_at desc limit 1000`,
         ...companyArgs,
       ).map((r) => ({