Add per-service system prompts with AI Settings tab view

Each feature service owns its system prompt in its config JSON on the
shared volume. The AI Settings page now has General and System Prompts
tabs — admins can view and edit any service's prompts at runtime with
changes taking effect within 30 s (config cache TTL).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/core/app_config.py

@@ -47,13 +47,46 @@ class AIServiceConfig(BaseModel):
 
 # ── Doc service config schemas ─────────────────────────────────────────────────
 
+_DOC_SYSTEM_PROMPT_DEFAULT = (
+    "You are a financial document analysis assistant. "
+    "Given the text extracted from a PDF document, return ONLY a JSON object "
+    "with no markdown, no code fences, and no explanation."
+)
+
+_DOC_USER_TEMPLATE_DEFAULT = (
+    'Analyze the following document text and return a JSON object with exactly these keys:\n'
+    'title (a short, descriptive human-readable title for this document, e.g. "ACME Corp Invoice April 2026", "Office Supplies Receipt", "Q1 Flower Delivery Order"),\n'
+    'document_type (one of: invoice, bill, receipt, order, expense, revenue, unknown),\n'
+    'total_amount (string or null),\n'
+    'currency (string or null),\n'
+    'vendor_name (string or null),\n'
+    'customer_name (string or null),\n'
+    'billing_address (string or null),\n'
+    'customer_address (string or null),\n'
+    'invoice_number (string or null),\n'
+    'invoice_date (string or null),\n'
+    'due_date (string or null),\n'
+    'tags (array of short keyword strings describing the document),\n'
+    'line_items (array of objects, each with keys: description, amount),\n'
+    'suggested_categories (array of 2 to 5 short category name strings a user might want to file this document under, e.g. "Utilities", "Travel", "Software Subscriptions", "Client Invoices").\n'
+    '\n'
+    'Document text:\n'
+    '{text}'
+)
+
 
 class DocumentsConfig(BaseModel):
     max_pdf_bytes: int = 20 * 1024 * 1024
 
 
+class DocServiceSystemPrompts(BaseModel):
+    system: str = _DOC_SYSTEM_PROMPT_DEFAULT
+    user_template: str = _DOC_USER_TEMPLATE_DEFAULT
+
+
 class DocServiceConfig(BaseModel):
     documents: DocumentsConfig = DocumentsConfig()
+    system_prompts: DocServiceSystemPrompts = DocServiceSystemPrompts()
 
 
 # ── Masking ────────────────────────────────────────────────────────────────────
@@ -134,3 +167,45 @@ def _merge_api_key(new_key: str, existing_key: str) -> str:
     if not new_key or "••••" in new_key:
         return existing_key
     return new_key
+
+
+# ── System prompts helpers ─────────────────────────────────────────────────────
+
+# Registry of all services that have editable system prompts.
+# key = service identifier, value = human-readable label
+SYSTEM_PROMPT_SERVICES: dict[str, str] = {
+    "doc_service": "Document Service",
+}
+
+
+def load_all_system_prompts() -> dict:
+    """Return {service_id: {label, system, user_template}} for all registered services."""
+    result: dict = {}
+    for service_id, label in SYSTEM_PROMPT_SERVICES.items():
+        config = load_service_config(service_id)
+        prompts = config.get("system_prompts", {})
+        defaults = _get_service_prompt_defaults(service_id)
+        result[service_id] = {
+            "label": label,
+            "system": prompts.get("system", defaults["system"]),
+            "user_template": prompts.get("user_template", defaults["user_template"]),
+        }
+    return result
+
+
+def save_service_system_prompts(service_id: str, system: str, user_template: str) -> None:
+    """Persist updated system prompts into the service's config file."""
+    if service_id not in SYSTEM_PROMPT_SERVICES:
+        raise ValueError(f"Unknown service: {service_id!r}")
+    config = load_service_config(service_id)
+    config.setdefault("system_prompts", {})
+    config["system_prompts"]["system"] = system
+    config["system_prompts"]["user_template"] = user_template
+    save_service_config(service_id, config)
+
+
+def _get_service_prompt_defaults(service_id: str) -> dict:
+    if service_id == "doc_service":
+        d = DocServiceSystemPrompts()
+        return {"system": d.system, "user_template": d.user_template}
+    return {"system": "", "user_template": ""}

backend/app/routers/settings.py

@@ -11,13 +11,16 @@ from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
 
 from app.core.app_config import (
+    SYSTEM_PROMPT_SERVICES,
     _merge_api_key,
     load_ai_service_config,
     load_ai_service_config_masked,
+    load_all_system_prompts,
     load_doc_service_config,
     load_doc_service_config_masked,
     save_ai_service_config,
     save_doc_service_config,
+    save_service_system_prompts,
 )
 from app.core.config import settings
 from app.deps import get_current_admin
@@ -45,6 +48,11 @@ class LimitsUpdate(BaseModel):
     max_pdf_mb: int
 
 
+class SystemPromptUpdate(BaseModel):
+    system: str
+    user_template: str
+
+
 # ── AI settings ────────────────────────────────────────────────────────────────
 
 
@@ -142,3 +150,29 @@ async def update_documents_limits(
     config.documents.max_pdf_bytes = body.max_pdf_mb * 1024 * 1024
     await asyncio.to_thread(save_doc_service_config, config)
     return load_doc_service_config_masked()
+
+
+# ── System prompts ─────────────────────────────────────────────────────────────
+
+
+@router.get("/system-prompts")
+async def get_system_prompts(
+    _: User = Depends(get_current_admin),
+) -> dict:
+    """Return all editable system prompts, keyed by service id."""
+    return await asyncio.to_thread(load_all_system_prompts)
+
+
+@router.patch("/system-prompts/{service_id}")
+async def update_system_prompt(
+    service_id: str,
+    body: SystemPromptUpdate,
+    _: User = Depends(get_current_admin),
+) -> dict:
+    """Update the system prompts for a single service."""
+    if service_id not in SYSTEM_PROMPT_SERVICES:
+        raise HTTPException(status_code=404, detail=f"No system prompts registered for {service_id!r}")
+    await asyncio.to_thread(
+        save_service_system_prompts, service_id, body.system, body.user_template
+    )
+    return await asyncio.to_thread(load_all_system_prompts)