>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3615557. --> Reported by: [camoa](https://www.drupal.org/user/2448054) Related to !51 >>> <h3>Problem/Motivation</h3> <p><code>AiPostGenerateSubscriber::getSubscribedEvents()</code> (<code>:61-66</code>) binds the same handler, <code>onPostGenerate</code>, to <strong>both</strong> <code>PostGenerateResponseEvent</code> and <code>PostStreamingResponseEvent</code>.</p> <p>For a streamed chat response both events fire, so <code>onPostGenerate</code> runs twice for a single AI call and <code>QuotaManager::logUsage()</code> inserts two rows into <code>ai_metering_usage</code> for that one call.</p> <p>Nothing deduplicates them. <code>ai_metering_usage</code> declares only a primary key on <code>id</code> plus non-unique indexes (<code>ai_metering.install:91-100</code>), the insert at <code>QuotaManager.php:175-177</code> is unconditional, and the module's only State-based dedup (<code>AiPreGenerateSubscriber.php:165-167</code>) gates <code>hook_ai_metering_quota_exceeded</code> invocation rather than the insert.</p> <p><strong>Consequence:</strong> for any site whose AI features stream &mdash; the default path for chat UIs and agent workflows &mdash; recorded tokens and cost are roughly doubled, and quota is consumed at twice the true rate. Unlike the cost-only defect in <a href="https://www.drupal.org/project/ai_metering/issues/3615553">#3615553</a>, this one also causes users to hit their quota early and be blocked from legitimate work.</p> <h3>Steps to reproduce</h3> <ol> <li>Configure any provider and trigger a <em>streamed</em> chat completion (for example through a chat UI that consumes the response as a stream, rather than a single blocking call).</li> <li>Inspect <code>ai_metering_usage</code> for that call, or the usage log at <code>/admin/reports/ai-metering</code>. Two rows appear for the single call. Compare against a non-streamed call, which produces one.</li> </ol> <h3>Environment</h3> <ul> <li>Drupal version: n/a &mdash; not reproduced on a running site, see AI assistance note</li> <li>ai_metering version: 1.0.x at commit a39fea9</li> <li>AI provider module + version: provider-independent &mdash; the double-binding is in this module, not in any provider</li> <li>AI feature module tested: none &mdash; found by code inspection; any streaming-capable feature module should exhibit it</li> </ul> <h3>Proposed resolution</h3> <p>Decide which event is authoritative for a streamed call and record once. Options worth weighing:</p> <ul> <li>Handle only <code>PostStreamingResponseEvent</code> for streamed calls, since token counts are not final until the stream is consumed.</li> <li>Persist an idempotency key so a repeat insert for the same call is recognised. The event already carries <code>requestThreadId</code> (available at <code>AiPostGenerateSubscriber.php:80</code>), but <code>ai_metering_usage</code> has no column for it.</li> </ul> <p>A unique key over the natural columns is <strong>not</strong> a valid fix: <code>ai_metering_usage</code> is an append-only event log, and two genuine identical calls by the same user in the same second are legitimate and must both persist.</p> <h3>Remaining tasks</h3> <ul> <li>Confirm empirically which events fire, and in what order, for a streamed call.</li> <li>Choose between event-selection and an idempotency key; the latter also guards future replay paths.</li> <li>Add test coverage for the streaming path &mdash; the existing suite does not assert that a streamed call produces exactly one usage row.</li> <li>Decide how to treat historical double-counted rows and any quota already consumed against them.</li> </ul> <h3>User interface changes</h3> <p>None directly. Recorded usage and cost will roughly halve for streaming sites once fixed.</p> <h3>API changes</h3> <p>None expected, unless an idempotency key is added to the public insert path.</p> <h3>Data model changes</h3> <p>Only if the idempotency-key option is chosen &mdash; that would add a column to <code>ai_metering_usage</code>. Historical duplicate rows remain unless a cleanup is written.</p> <h3>AI assistance</h3> <p>AI-Generated: Yes (Claude Code &mdash; multi-agent code analysis located this defect while paper-testing a different, incorrect claim about duplicate rows; this issue text was drafted with AI assistance). No module code was generated. Every claim is code-cited and was reviewed before filing; the citations can be checked against the referenced lines.</p>