phase 44 (part 1): migrate TS callers to /v1/chat + add regression guard

Migrates the four TypeScript /generate callers to the gateway's
/v1/chat surface so every LLM call lands on /v1/usage and Langfuse:

  tests/multi-agent/agent.ts::generate()      provider="ollama"
  tests/agent_test/agent_harness.ts::callAgent provider="ollama"
  bot/propose.ts::generateProposal             provider="ollama_cloud"
  mcp-server/observer.ts (error analysis)      provider="ollama"

Each migration follows the same pattern as the prior generateCloud()
migration (already on /v1/chat from 2026-04-24): replace
`fetch(SIDECAR/generate)` with `fetch(GATEWAY/v1/chat)`, swap the
prompt-style body for OpenAI-compat messages array, extract
content from `choices[0].message.content` instead of `text`.

Same upstream models in every case — gateway is the new home for
the call, transport otherwise unchanged.

Adds scripts/check_phase44_callers.sh — fail-loud regression guard
that exits non-zero if any non-adapter file fetches /generate or
api/generate. Adapter files (crates/gateway, crates/aibridge,
sidecar/) are exempt. Pre-tightening regex flagged prose mentions
in comments; the shipped regex requires `fetch(...)` or
`client.post(...)` shape so comments don't trip it.

Verification:
  bun build mcp-server/observer.ts                       compiles
  bun build tests/multi-agent/agent.ts                   compiles
  bun build tests/agent_test/agent_harness.ts            compiles
  bun build bot/propose.ts                               compiles
  ./scripts/check_phase44_callers.sh                     ✅ clean
  systemctl restart lakehouse-observer                   active

Phase 44 part 2 (deferred):
  - crates/aibridge/src/client.rs:118 still posts to sidecar /generate
    directly. AiClient is the foundational Rust LLM caller used by
    8+ vectord modules; migrating it is a workspace-wide refactor
    that needs its own commit. Plan: keep AiClient as the local-
    transport layer for the gateway's `provider=ollama` arm, but
    introduce a thin `/v1/chat` wrapper for external callers (vectord
    autotune, agent, rag, refresh, supervisor, playbook_memory).
  - tests/real-world/hard_task_escalation.ts: comment mentions
    /api/generate but doesn't actually call it. Comment is left
    intentionally as historical context; regex no longer flags it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bot/propose.ts

@@ -13,7 +13,12 @@ import { readFile } from "node:fs/promises";
 import { createHash } from "node:crypto";
 import type { Gap, Proposal } from "./types.ts";
 
-const SIDECAR_URL = process.env.LH_SIDECAR_URL ?? "http://localhost:3200";
+// Phase 44 migration (2026-04-27): bot/propose.ts now flows through
+// the gateway's /v1/chat instead of hitting the sidecar's /generate
+// directly. /v1/usage tracks the call, Langfuse traces it, observer
+// sees it. Same upstream model (CLOUD_MODEL gpt-oss:120b on
+// Ollama Cloud) — gateway just owns the routing.
+const GATEWAY_URL = process.env.LH_GATEWAY_URL ?? "http://localhost:3100";
 const REPO_ROOT = "/home/profit/lakehouse";
 const PRD_PATH = `${REPO_ROOT}/docs/PRD.md`;
 const CLOUD_MODEL = process.env.LH_BOT_MODEL ?? "gpt-oss:120b";
@@ -72,13 +77,16 @@ export async function generateProposal(gap: Gap, historySummary: string = ""): P
   sections.push("Propose a small change that addresses this gap. Respond with the JSON object only.");
   const userPrompt = sections.join("\n");
 
-  const r = await fetch(`${SIDECAR_URL}/generate`, {
+  const r = await fetch(`${GATEWAY_URL}/v1/chat`, {
     method: "POST",
     headers: { "content-type": "application/json" },
     body: JSON.stringify({
       model: CLOUD_MODEL,
-      system: SYSTEM_PROMPT,
-      prompt: userPrompt,
+      provider: "ollama_cloud",
+      messages: [
+        { role: "system", content: SYSTEM_PROMPT },
+        { role: "user", content: userPrompt },
+      ],
       temperature: 0.2,
       max_tokens: MAX_TOKENS,
       think: false,
@@ -86,10 +94,10 @@ export async function generateProposal(gap: Gap, historySummary: string = ""): P
     signal: AbortSignal.timeout(180000), // cloud T3 can be slow — 3 min
   });
   if (!r.ok) {
-    throw new Error(`sidecar ${r.status}: ${await r.text()}`);
+    throw new Error(`gateway /v1/chat ${r.status}: ${await r.text()}`);
   }
   const j = await r.json() as any;
-  const raw: string = j.text ?? j.response ?? "";
+  const raw: string = j?.choices?.[0]?.message?.content ?? "";
   const usage = j.usage ?? {};
   const tokens = (usage.prompt_tokens ?? 0) + (usage.completion_tokens ?? 0);