clinic_id          text  — indexed, no FK (integrity via authenticated session)
period_start       text  — "YYYY-MM-DD", start of current billing period (PK part)
monthly_studies    integer  default 0
daily_studies      integer  default 0
day_key            text  — "YYYY-MM-DD", tracks which day daily_studies covers
tokens_input       integer  default 0
tokens_output      integer  default 0
updated_at         timestamp

UPDATE dicom_quota
SET daily_studies = 0, day_key = today, updated_at = now
WHERE clinic_id = ? AND period_start = ?

anchor_day = day_of_month(module.created_at)   -- e.g. 15
current_period_start = most recent date where day_of_month = anchor_day, on or before today
next_reset = current_period_start + 1 month

dicom_ai_terms_accepted_at   timestamp  nullable

{ patientFileId, imageBase64, modality?, bodyPart?, sliceCount?: number }

1. Compute period_start from clinic_modules.created_at anchor
2. Load (or create) dicom_quota row; apply daily reset if day_key ≠ today
3. Check monthly_studies >= 500         → 429 { reason: "monthly_studies" }
4. Check (tokens_input + tokens_output) >= 5_000_000 → 429 { reason: "monthly_tokens" }
5. Check daily_studies >= 20            → 429 { reason: "daily_studies" }
6. Check sliceCount > 30                → 400 { reason: "slice_limit" }
7. Acquire concurrency slot via clinic-hub DO
   → if activeAnalyses >= 3            → 429 { reason: "concurrent" }
8. Call analyzeDicomImage() with max_completion_tokens: 1000, temperature: 0.2
9. On success: UPDATE dicom_quota — increment monthly_studies, daily_studies,
   tokens_input += result.usage.input_tokens,
   tokens_output += result.usage.output_tokens
10. Release concurrency slot (always, in finally block)

{
  "error": "quota_exceeded",
  "reason": "monthly_studies | monthly_tokens | daily_studies | concurrent",
  "limit": 500,
  "used": 500,
  "resetsAt": "2026-05-15T00:00:00Z"
}

{
  "monthly_studies": 312,
  "monthly_limit": 500,
  "daily_studies": 8,
  "daily_limit": 20,
  "tokens_input": 2_100_000,
  "tokens_output": 480_000,
  "tokens_limit": 5_000_000,
  "period_start": "2026-04-15",
  "next_reset": "2026-05-15",
  "terms_accepted": true
}

private activeAnalyses = 0;
private slotTimestamps = new Map<string, number>(); // requestId → acquired_at ms

acquireAnalysisSlot(requestId: string): { granted: boolean; active: number } {
  this.sweepStaleSlots(); // lazy cleanup — only runs when someone tries to acquire
  if (this.activeAnalyses >= 3) return { granted: false, active: this.activeAnalyses };
  this.activeAnalyses++;
  this.slotTimestamps.set(requestId, Date.now());
  return { granted: true, active: this.activeAnalyses };
}

releaseAnalysisSlot(requestId: string): void {
  if (this.slotTimestamps.has(requestId)) {
    this.slotTimestamps.delete(requestId);
    this.activeAnalyses = Math.max(0, this.activeAnalyses - 1);
  }
}

private sweepStaleSlots(): void {
  const cutoff = Date.now() - 5 * 60 * 1000; // 5 minutes
  for (const [id, ts] of this.slotTimestamps) {
    if (ts < cutoff) {
      this.slotTimestamps.delete(id);
      this.activeAnalyses = Math.max(0, this.activeAnalyses - 1);
    }
  }
}

AI Analyses  ████████░░  312 / 500  ·  Resets 15 May
             8 / 20 today

⚠  AI-generated analysis — A licensed dentist must review all findings
   and make all clinical decisions. This is not a clinical diagnosis.

[Brain icon]  DICOM AI Analysis
              Ruby analysed [filename] · [modality] · [urgencyLevel] urgency
              [timestamp]   [View report →]

[
  {
    "clinic_id": "...",
    "clinic_name": "Bright Smiles Dental",
    "period_start": "2026-04-15",
    "next_reset": "2026-05-15",
    "monthly_studies": 312,
    "daily_studies": 8,
    "tokens_input": 2_100_000,
    "tokens_output": 480_000,
    "terms_accepted_at": "2026-04-16T09:23:00Z"
  }
]