docs(revamp): add Capabilities domain (typed verbs)

plans/backend/revamp/01-capabilities.md

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+# Domain ① — Capabilities (CI pivot revamp · WIP)
+
+> **WIP design doc.** Part of the Phase 4 → end revamp (the old "pipeline").
+> **Scope guardrail:** Phases 1–3 are **SHIPPED and FIXED** — the rename, and the proprietary
+> crawler/proxy/billing/stealth/captcha stack. This domain *builds on* them and never modifies them.
+
+## Role in the universe
+
+```
+FIXED foundation (done):  Acquisition (crawler moat) · Metering (03c) · Identity/Tenancy
+OUR scope (this revamp):  ▶ Capabilities ◀ → Access → Intelligence + Timeline → Triggers
+```
+
+Capabilities sits directly on the fixed foundation and is consumed by **Access** (the doors) and
+the **Intelligence** hot loop. It is the first domain because everything above it calls into it.
+
+## Purpose
+
+Turn the fixed Acquisition engine (+ a new Google Maps actor) into a **small set of typed,
+callable verbs** that every door (chat / REST / MCP) and the Intelligence loop consume
+**identically**.
+
+This is the core pivot of old Phase 4: **replace "connector that ingests into the KB" with
+"capability that returns data."** A capability is a stateless function you *call and get data
+back from* — no `SearchSourceConnector` row to configure, no KB write, no schedule attached.
+
+## Foundation it builds on (do not touch)
+
+- `WebCrawlerConnector.crawl_url(url) -> CrawlOutcome` — single-URL fetch; `{content, metadata,
+  crawler_type}` on `SUCCESS`; billable predicate single-sourced as `status == SUCCESS`.
+  (`app/proprietary/web_crawler/`.)
+- `WebCrawlCreditService` (`03c`) — per-success metering + the `bill=` seam.
+- Proxy / stealth / captcha tiers — all behind `crawl_url`; callers never see the tier.
+
+## The verb set (MVP) — namespaced, nothing top-level
+
+Two namespaces: **`web.*`** (generic crawler product) and **`maps.*`** (the one platform actor).
+Future platforms slot in as their own namespace (`linkedin.*`, `amazon.*`, …).
+
+| Verb | Input → Output | Mode | Executes over | Bills (03c) |
+|------|----------------|------|---------------|-------------|
+| `web.scrape(urls[])` | → `[{url, status, content, metadata}]` | inline-or-job | loop `crawl_url` | per success |
+| `web.discover(query, top_k)` | → `[{url, title, snippet, provider}]` | inline | search providers (SearXNG/Linkup/Baidu) | per search *(or free — open)* |
+| `maps.search(query, location)` | → `[place]` | job | Maps actor *(new, proprietary)* | per place |
+| `maps.place(place_id\|url)` | → `place` (structured) | inline | Maps actor *(new, proprietary)* | 1 |
+| `maps.reviews(place)` | → `[review]` (paged) | job | Maps actor *(new, proprietary)* | per page |
+
+## `web.scrape` — one array-friendly verb (no separate "batch")
+
+Scraping always **welcomes an array of URLs**. There is no separate `scrape_batch`. One verb,
+one mental model: "give me URLs, I give you per-URL content."
+
+## Execution mode — a property of the **result**, not two verbs
+
+A capability does **not** split into sync/async variants. Every call returns a **uniform result
+envelope**:
+
+```
+{ status: "completed" | "pending", job_id?: str, progress?: {done, total}, results?: [...] , error?: ... }
+```
+
+- **inline (fast path):** small/fast input → finishes in-request → envelope returns `completed`
+  with `results` inline → **zero polling**. (single page, one place, a search)
+- **job (slow path):** large/slow input → envelope returns `pending` + `job_id` → caller polls a
+  status endpoint until `completed`, then reads `results`. (batch scrape, Maps search/reviews)
+
+So "sync" is simply *a job that finished instantly*. Same verb, same response shape, no magic
+branching for the caller to reason about.
+
+- **Threshold** (how many URLs / how heavy before it goes async) is **configurable**.
+- A caller may pass `async: true` to **force** a job even for small input (agents that never want
+  to block).
+- **Only infra this requires:** a thin **job record** (`id, status, progress, result_ref`) + the
+  **existing Celery workers**. *Not* a resurrected `pipeline_runs`. Sync verbs need none of it.
+
+## The capability registry — single source of truth
+
+One registry entry per verb:
+
+```
+Capability {
+  name            # dotted, e.g. "web.scrape", "maps.search"
+  input_schema    # Pydantic
+  output_schema   # Pydantic
+  mode            # can-complete-inline?  +  job-capable?
+  executor        # the async fn (wraps Acquisition / Maps actor)
+  billing_unit    # how Metering charges this call
+}
+```
+
+The **three doors are generated from the registry**, not hand-written three times:
+
+- **chat tool** ← entry (tool def + handler)
+- **REST route** ← entry (path + request/response models)
+- **MCP tool** ← entry (MCP tool schema + handler)
+
+…and the **Intelligence** hot loop calls the *same* `executor` directly. Add a verb once → it
+lights up on every surface; the I/O contract cannot drift between surfaces.
+
+## Where it lives / license boundary
+
+- New **Apache-2** package `app/capabilities/` (registry, schemas, executors, the thin job store).
+- It **imports from** the proprietary Acquisition engine but never moves into it.
+- The **Maps extractor logic is proprietary** (`app/proprietary/...`), consumed by the `maps.*`
+  executors — same boundary rule Phase 3 set (Apache code may import *from* proprietary, not move
+  *into* it).
+
+## Billing integration — open to the billing service (not hardcoded per verb)
+
+Billing is **not** baked into each verb. A capability only **declares a `billing_unit`** in its
+registry entry; charging is delegated to the **billing service**, so adding/repricing a unit is a
+billing-service concern, not a capability rewrite. `03c`'s `WebCrawlCreditService` is the **first
+provider**; new units register with the same service.
+
+- `web.scrape` → per `SUCCESS` (existing `web_crawl` unit).
+- `maps.*` → register a new per-place / per-page unit **with the billing service** (same wallet).
+- captcha attempts → existing per-attempt `web_crawl_captcha` unit (unchanged).
+- `web.discover` → register a per-search unit (or mark free) **with the billing service**.
+
+The point: the registry says *"this verb bills unit X"*; the **billing service owns what unit X
+costs and how it settles.** Verbs stay pure; pricing stays pluggable.
+
+## The Maps actor (clarification)
+
+- **Google-Maps-agnostic** — works for *any* place type (restaurants, gyms, hotels, retail, …).
+- Returns **typed structured objects** (`{name, rating, review_count, hours, price_level, …}`),
+  not raw markdown — which is exactly what the Intelligence/Timeline layer needs to diff reliably.
+- The "restaurant" use case is an **Intelligence-domain wedge** (one Tracker), **not** a constraint
+  on the capability. The capability never knows what decision it serves.
+
+## Relationship to the drafted Phase 4
+
+- **04b (source-discovery)** → **absorbed** as `web.discover` + relocating Linkup/Baidu keys from
+  per-connector `config` to platform env (SearXNG already env-based). Tavily/Serper dropped.
+- **04a (connector taxonomy + MCP routing)** → **demoted to backward-compat hygiene.** The
+  capability registry is the new spine, so the Type-1/Type-2 *connector* registry is no longer
+  central. 04a's "turn off branded connectors" stays a small, separable cleanup for the legacy
+  chat agent; the **BYO-`MCP_CONNECTOR`** routing fix belongs to the **Access/Conversation** domain
+  (it lets the agent use the *user's* external tools — a different concept from our capabilities).
+
+## Deferred (not in MVP)
+
+- **Recursive site crawl** (follow links across a whole site) — doesn't exist today; the
+  "crawl a topic" story is `web.discover` → `web.scrape`.
+- A generic **`web.extract`** (LLM-structured extraction as a standalone verb) — structured
+  extraction lives in the Intelligence loop for MVP; promote to a capability later if devs want it.
+- Additional platform namespaces (`linkedin.*`, `amazon.*`, …).
+
+## Locked decisions
+
+1. Verbs: `web.scrape` · `web.discover` · `maps.search` · `maps.place` · `maps.reviews`. Namespaced; nothing top-level.
+2. One array-friendly `web.scrape` (no separate batch verb).
+3. Execution mode = result property (uniform `completed`/`pending` envelope), not separate verbs.
+4. Build the thin job model now (Maps search / batch scrape force it).
+5. One capability registry → generates chat/REST/MCP doors + feeds the Intelligence executor.
+6. `app/capabilities/` Apache-2; Maps extractor proprietary; billing **delegated to the billing
+   service** (verbs declare a `billing_unit`; `03c` is the first provider, new units register there).
+7. Connector → capability is a **replacement** for these data sources, not an extension.
+
+## Open questions (carry forward)
+
+- Default async threshold for `web.scrape`.
+- The **Google Maps actor** is **net-new** (not part of shipped Phases 1–3) — designed/built as a
+  **separate effort** (incl. sourcing legality). `maps.*` verbs are contracts against it; this domain
+  doesn't block on it.