feat: Multi-agent database primitives — batch queries + session agent info

[chubes4]

Summary

The agent database layer assumes single-agent-per-user throughout. To support multi-agent frontend chat (agent switching, personal agents, multi-agent views), several DB-level primitives are missing.

Related: #972 (per-user dynamic toolsets), #919 (scoped agent creation)

Gap 1: No get_all_by_owner_id() on Agents repository

File: inc/Core/Database/Agents/Agents.php

get_by_owner_id() is hard-coded to LIMIT 1 (line 137). There is no way to list all agents a user owns without fetching the entire agents table:

// Current workaround in AgentAbilities::createAgent() line 503:
$all_agents = $agents_repo->get_all();
$owned = array_filter($all_agents, fn($a) => (int) $a['owner_id'] === $owner_id);

This fetches every agent in the system and filters in-memory. Completely wrong at scale.

Needed

public function get_all_by_owner_id(int $owner_id): array {
    $rows = $this->wpdb->get_results(
        $this->wpdb->prepare(
            'SELECT * FROM %i WHERE owner_id = %d ORDER BY agent_id ASC',
            $this->table_name,
            $owner_id
        ),
        ARRAY_A
    );
    // ...decode agent_config...
    return $rows ?: [];
}

Also fix AgentAbilities::createAgent() to use this instead of get_all() + array_filter.

Gap 2: No get_agents_by_ids() batch method

File: inc/Core/Database/Agents/Agents.php

AgentAccess::get_agent_ids_for_user() returns int[] — just IDs. To get full agent rows, callers must make N+1 queries via get_agent() in a loop. This pattern exists in Api/Agents.php::handle_list() for non-admin users.

Needed

public function get_agents_by_ids(array $agent_ids): array {
    if (empty($agent_ids)) return [];
    $placeholders = implode(',', array_fill(0, count($agent_ids), '%d'));
    $rows = $this->wpdb->get_results(
        $this->wpdb->prepare(
            "SELECT * FROM %i WHERE agent_id IN ({$placeholders}) ORDER BY agent_id ASC",
            array_merge([$this->table_name], $agent_ids)
        ),
        ARRAY_A
    );
    // ...decode agent_config...
    return $rows ?: [];
}

Gap 3: get_user_sessions() strips agent_id from response

File: inc/Core/Database/Chat/Chat.php lines 507-528

The SELECT * query fetches agent_id from the row, but the return array mapping discards it:

$result[] = [
    'session_id'    => $session['session_id'],
    'title'         => $session['title'] ?? null,
    'context'       => $session['context'] ?? 'chat',
    'first_message' => mb_substr($first_message, 0, 100),
    'message_count' => count($messages),
    'created_at'    => ...,
    'updated_at'    => ...,
    // agent_id is NOT included
];

The frontend cannot display which agent a session belongs to, making multi-agent session lists impossible.

Needed

1. Add agent_id to the return array
2. Enrich with agent_name/agent_slug via batch post-query lookup using get_agents_by_ids()

Gap 4: get_all() has no owner_id filter

File: inc/Core/Database/Agents/Agents.php lines 269-306

get_all() accepts $args['site_id'] but ignores any owner_id parameter. Should support $args['owner_id'] for filtered queries.

Gap 5: PermissionHelper::resolve_scoped_agent_id() returns only first agent

File: inc/Abilities/PermissionHelper.php lines 379-425

This method finds ONE agent via get_by_owner_id() (LIMIT 1) or takes the first from get_agent_ids_for_user(). For multi-agent, a companion resolve_all_accessible_agent_ids() is needed.

Checklist

• Add Agents::get_all_by_owner_id(int $owner_id): array
• Add Agents::get_agents_by_ids(array $agent_ids): array
• Add owner_id support to Agents::get_all() args
• Add agent_id (+ optionally agent_name, agent_slug) to Chat::get_user_sessions() return shape
• Fix AgentAbilities::createAgent() to use get_all_by_owner_id() instead of get_all() + array_filter
• Add PermissionHelper::resolve_all_accessible_agent_ids() or equivalent