diff --git a/docs/cli.md b/docs/cli.md
index 165be36e..2e076040 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -273,7 +273,7 @@ are stored under `.lousho/` in the current directory. See
 ```bash
 npx lousho observe start                        # collector on http://127.0.0.1:7777
 npx lousho observe status                       # health + fleet counts
-npx lousho observe stop                         # pidfile + SIGTERM
+npx lousho observe stop                         # <db>.pid + SIGTERM (checks the daemon serves --db)
 npx lousho observe rebuild-rollups              # recompute insight aggregates
 npx lousho observe token create --project myapp # bearer key for non-loopback auth
 ```
@@ -283,7 +283,13 @@ set: traces, fleet monitoring, eval scores, the prompt registry and the
 context hub in one SQLite file (default `~/.lousho/observe.db`). The Studio
 Observe tabs read it. `start` takes `--port` (or `LOUSHO_OBSERVE_PORT`),
 `--db`, `--host`, `--require-token` and a repeatable `--webhook` for alert
-hooks. See [The observe daemon](./observability.md#the-observe-daemon).
+hooks. Each daemon writes its own `<db name>.pid` beside the db
+(`observe.db` gives `observe.pid`), so two dbs in one folder never share a
+pidfile. `start` exits 1 when the port already serves a different db, and
+`stop` refuses to signal when the daemon at the pidfile's port reports another
+db, and falls back to signalling when it cannot verify (unreachable, or an old
+one-line pidfile). See
+[The observe daemon](./observability.md#the-observe-daemon).
 
 ## `lousho prompt`
 
diff --git a/llms-full.txt b/llms-full.txt
index 2a367a48..788cd04e 100644
--- a/llms-full.txt
+++ b/llms-full.txt
@@ -5150,7 +5150,7 @@ are stored under `.lousho/` in the current directory. See
 ```bash
 npx lousho observe start                        # collector on http://127.0.0.1:7777
 npx lousho observe status                       # health + fleet counts
-npx lousho observe stop                         # pidfile + SIGTERM
+npx lousho observe stop                         # <db>.pid + SIGTERM (checks the daemon serves --db)
 npx lousho observe rebuild-rollups              # recompute insight aggregates
 npx lousho observe token create --project myapp # bearer key for non-loopback auth
 ```
@@ -5160,7 +5160,13 @@ set: traces, fleet monitoring, eval scores, the prompt registry and the
 context hub in one SQLite file (default `~/.lousho/observe.db`). The Studio
 Observe tabs read it. `start` takes `--port` (or `LOUSHO_OBSERVE_PORT`),
 `--db`, `--host`, `--require-token` and a repeatable `--webhook` for alert
-hooks. See [The observe daemon](https://github.com/LinuxDevil/agent-sdk/blob/main/docs/observability.md#the-observe-daemon).
+hooks. Each daemon writes its own `<db name>.pid` beside the db
+(`observe.db` gives `observe.pid`), so two dbs in one folder never share a
+pidfile. `start` exits 1 when the port already serves a different db, and
+`stop` refuses to signal when the daemon at the pidfile's port reports another
+db, and falls back to signalling when it cannot verify (unreachable, or an old
+one-line pidfile). See
+[The observe daemon](https://github.com/LinuxDevil/agent-sdk/blob/main/docs/observability.md#the-observe-daemon).
 
 ## `lousho prompt`
 
diff --git a/src/cli/observe.test.ts b/src/cli/observe.test.ts
index 911b137a..52c6381a 100644
--- a/src/cli/observe.test.ts
+++ b/src/cli/observe.test.ts
@@ -64,7 +64,8 @@ describe('lousho observe', () => {
   });
 
   it('start on the daemon\'s own port reports "already running" and exits 0', async () => {
-    const daemon = await start();
+    const daemon = await startObserveDaemon({ dbPath: dbPath(), port: 0 });
+    daemons.push(daemon);
     expect(await runObserve(['start', '--port', String(daemon.port), '--db', dbPath()])).toBe(0);
     expect(logs.at(-1)).toContain('already running');
   });
@@ -93,6 +94,38 @@ describe('lousho observe', () => {
     expect(fs.existsSync(pidPath)).toBe(false);
   });
 
+  it('start --db b.db against a daemon serving a.db exits 1 naming the other db', async () => {
+    const a = path.join(cwd, 'a.db');
+    const daemon = await startObserveDaemon({ dbPath: a, port: 0 });
+    daemons.push(daemon);
+    expect(await runObserve(['start', '--port', String(daemon.port), '--db', path.join(cwd, 'b.db')])).toBe(1);
+    expect(errors.at(-1)).toContain(`port ${daemon.port} is serving ${path.resolve(a)}`);
+    // the same db is still "already running"
+    expect(await runObserve(['start', '--port', String(daemon.port), '--db', a])).toBe(0);
+    expect(logs.at(-1)).toContain('already running');
+  });
+
+  it('stop --db a.db does not signal a pid whose daemon serves b.db', async () => {
+    const b = await startObserveDaemon({ dbPath: path.join(cwd, 'b.db'), port: 0 });
+    daemons.push(b);
+    const a = path.join(cwd, 'a.db');
+    fs.writeFileSync(defaultPidPath(a), `${process.pid}\n${b.port}\n`);
+    const kill = vi.spyOn(process, 'kill').mockImplementation(() => true);
+    expect(await runObserve(['stop', '--db', a])).toBe(1);
+    expect(kill).not.toHaveBeenCalled();
+    expect(errors.at(-1)).toContain('serves');
+    expect(fs.existsSync(defaultPidPath(a))).toBe(true);
+  });
+
+  it('stop signals the pid when its daemon serves this db', async () => {
+    const a = path.join(cwd, 'a.db');
+    const d = await startObserveDaemon({ dbPath: a, port: 0, pidPath: defaultPidPath(a) });
+    daemons.push(d);
+    const kill = vi.spyOn(process, 'kill').mockImplementation(() => true);
+    expect(await runObserve(['stop', '--db', a])).toBe(0);
+    expect(kill).toHaveBeenCalledWith(process.pid, 'SIGTERM');
+  });
+
   it('rebuild-rollups rebuilds the buckets of a local db', async () => {
     expect(await runObserve(['rebuild-rollups', '--db', dbPath()])).toBe(0);
     expect(logs.at(-1)).toContain('rebuilt');
diff --git a/src/cli/observe.ts b/src/cli/observe.ts
index 78b3e0b5..61446e30 100644
--- a/src/cli/observe.ts
+++ b/src/cli/observe.ts
@@ -21,6 +21,7 @@ import {
   defaultDbPath,
   defaultPidPath,
   isObserveDaemon,
+  sameDbPath,
   probeHealth,
   startObserveDaemon,
   type HealthProbe,
@@ -114,6 +115,25 @@ function envPort(): number {
 
 /* ------------------------------------------------------------------- start */
 
+/** `start` hit EADDRINUSE: say who owns the port. 0 = this db's daemon already runs; 1 = anything else. */
+async function reportPortInUse(port: number, host: string, dbPath: string): Promise<number> {
+  const health = await probeHealth(port, host);
+  if (!isObserveDaemon(health)) {
+    console.error(
+      `lousho observe: port ${port} is taken by another service (its /health is not ${OBSERVE_SERVICE}). Pass --port <free>, or stop that service.`
+    );
+    return 1;
+  }
+  if (health.db !== undefined && !sameDbPath(health.db, dbPath)) {
+    console.error(
+      `lousho observe: port ${port} is serving ${health.db}, not ${dbPath}. Pass --port <free> for this db, or stop that daemon first.`
+    );
+    return 1;
+  }
+  console.log(`lousho observe: already running on http://${host}:${port} (service ${OBSERVE_SERVICE}, version ${health.version ?? 'unknown'}).`);
+  return 0;
+}
+
 async function runStart(args: string[]): Promise<number> {
   const spec = SUB_SPECS.start;
   const { values, help } = parseCommand(spec, args);
@@ -132,17 +152,7 @@ async function runStart(args: string[]): Promise<number> {
   try {
     daemon = await startObserveDaemon({ dbPath, port, host, requireToken, pidPath, webhooks });
   } catch (error) {
-    if ((error as NodeJS.ErrnoException).code === 'EADDRINUSE') {
-      const health = await probeHealth(port, host);
-      if (isObserveDaemon(health)) {
-        console.log(`lousho observe: already running on http://${host}:${port} (service ${OBSERVE_SERVICE}, version ${health.version ?? 'unknown'}).`);
-        return 0;
-      }
-      console.error(
-        `lousho observe: port ${port} is taken by another service (its /health is not ${OBSERVE_SERVICE}). Pass --port <free>, or stop that service.`
-      );
-      return 1;
-    }
+    if ((error as NodeJS.ErrnoException).code === 'EADDRINUSE') return reportPortInUse(port, host, dbPath);
     throw error;
   }
 
@@ -215,6 +225,36 @@ async function runStatus(args: string[]): Promise<number> {
 
 /* -------------------------------------------------------------------- stop */
 
+/** The pidfile's pid (line 1) and, for newer daemons, the port it listens on (line 2). */
+function readPidfile(pidPath: string): { pid?: number; port?: number } {
+  let text: string;
+  try {
+    text = fs.readFileSync(pidPath, 'utf8');
+  } catch {
+    return {};
+  }
+  const [pidLine = '', portLine] = text.split(/\r?\n/);
+  const pid = Number(pidLine.trim());
+  const port = Number(portLine?.trim());
+  return {
+    ...(Number.isInteger(pid) && pid > 0 ? { pid } : {}),
+    ...(Number.isInteger(port) && port > 0 ? { port } : {}),
+  };
+}
+
+/**
+ * What the daemon at the pidfile's port serves when that is not `dbPath`
+ * (a different db, or another service); `undefined` when it matches or cannot
+ * be verified (no port recorded, nothing answers).
+ */
+async function stopMismatch(port: number | undefined, dbPath: string): Promise<string | undefined> {
+  if (port === undefined) return undefined;
+  const health = await probeHealth(port);
+  if (health === undefined) return undefined;
+  if (!isObserveDaemon(health)) return 'another service';
+  return health.db !== undefined && !sameDbPath(health.db, dbPath) ? health.db : undefined;
+}
+
 async function runStop(args: string[]): Promise<number> {
   const spec = SUB_SPECS.stop;
   const { values, help } = parseCommand(spec, args);
@@ -224,18 +264,20 @@ async function runStop(args: string[]): Promise<number> {
   }
   const dbPath = dbPathOf(values.db);
   const pidPath = defaultPidPath(dbPath);
-  let pid: number | undefined;
-  try {
-    pid = Number(fs.readFileSync(pidPath, 'utf8').trim());
-  } catch {
-    pid = undefined;
-  }
-  if (pid === undefined || !Number.isInteger(pid) || pid <= 0) {
+  const { pid, port: pidPort } = readPidfile(pidPath);
+  if (pid === undefined) {
     console.error(
       `lousho observe: no pidfile at ${pidPath}. If a daemon is running, stop it with Ctrl+C (or 'kill <pid>' / Task Manager).`
     );
     return 1;
   }
+  const mismatch = await stopMismatch(pidPort, dbPath);
+  if (mismatch !== undefined) {
+    console.error(
+      `lousho observe: pid ${pid} in ${pidPath} serves ${mismatch}, not ${dbPath}; not signalling it. Remove the stale pidfile if it is wrong.`
+    );
+    return 1;
+  }
   try {
     process.kill(pid, 'SIGTERM');
   } catch (error) {
diff --git a/src/observe/daemon.test.ts b/src/observe/daemon.test.ts
index e6f0cd97..3f36bfb0 100644
--- a/src/observe/daemon.test.ts
+++ b/src/observe/daemon.test.ts
@@ -5,9 +5,10 @@
  * port-collision detection.
  */
 import { afterEach, describe, expect, it } from 'vitest';
-import { isObserveDaemon, probeHealth, startObserveDaemon, type ObserveDaemon } from './daemon';
+import * as nodePath from 'node:path';
+import { defaultPidPath, isObserveDaemon, probeHealth, sameDbPath, startObserveDaemon, type ObserveDaemon } from './daemon';
 import { OBSERVE_SERVICE } from './envelope';
-import { createToken } from './store';
+import { createToken, openDb } from './store';
 
 const T0 = 1_700_000_000_000;
 
@@ -57,6 +58,24 @@ describe('GET /health', () => {
   });
 });
 
+describe('per-db pidfile and db identity', () => {
+  it('names the pidfile after the db so two dbs in one folder never share it', () => {
+    expect(defaultPidPath('/d/a.db')).toBe(nodePath.resolve('/d/a.pid'));
+    expect(defaultPidPath('/d/b.db')).toBe(nodePath.resolve('/d/b.pid'));
+    expect(defaultPidPath('/d/observe.db')).toBe(nodePath.resolve('/d/observe.pid'));
+    expect(defaultPidPath('/d/data.sqlite')).toBe(nodePath.resolve('/d/data.sqlite.pid'));
+  });
+
+  it('/health reports the absolute db path; sameDbPath compares resolved paths', async () => {
+    const daemon = await start({ dbPath: 'mem-test.db', db: openDb(':memory:') });
+    const health = await probeHealth(daemon.port);
+    expect(health?.db).toBe(nodePath.resolve('mem-test.db'));
+    expect(sameDbPath(health?.db, 'mem-test.db')).toBe(true);
+    expect(sameDbPath(health?.db, 'other.db')).toBe(false);
+    expect(sameDbPath(undefined, 'other.db')).toBe(false);
+  });
+});
+
 describe('POST /api/v1/ingest', () => {
   it('accepts a batch and serves it back through the read endpoints', async () => {
     const daemon = await start();
diff --git a/src/observe/daemon.ts b/src/observe/daemon.ts
index 794c8722..2b563e7c 100644
--- a/src/observe/daemon.ts
+++ b/src/observe/daemon.ts
@@ -34,9 +34,23 @@ export function defaultDbPath(homeDir: string = os.homedir()): string {
   return path.join(homeDir, '.lousho', 'observe.db');
 }
 
-/** Where the pidfile goes for a given db path (same directory, fixed name). */
+/**
+ * Where the pidfile goes for a given db path: `<dir>/<db name without .db>.pid`,
+ * so two daemons whose dbs share a folder never share a pidfile
+ * (`observe.db` keeps `observe.pid`).
+ */
 export function defaultPidPath(dbPath: string): string {
-  return path.join(path.dirname(resolveForFs(dbPath)), 'observe.pid');
+  const resolved = resolveForFs(dbPath);
+  const base = path.basename(resolved);
+  const stem = base.toLowerCase().endsWith('.db') && base.length > 3 ? base.slice(0, -3) : base;
+  return path.join(path.dirname(resolved), `${stem}.pid`);
+}
+
+/** Whether two db paths name the same file (resolved; case-insensitive on win32). */
+export function sameDbPath(a: string | undefined, b: string): boolean {
+  if (a === undefined) return false;
+  const norm = (p: string): string => (process.platform === 'win32' ? resolveForFs(p).toLowerCase() : resolveForFs(p));
+  return norm(a) === norm(b);
 }
 
 function resolveForFs(p: string): string {
@@ -154,6 +168,7 @@ export async function startObserveDaemon(options: ObserveDaemonOptions = {}): Pr
     let bodyRead: Promise<string> | undefined;
     const ctx: RouteContext = {
       db,
+      dbPath,
       req,
       res,
       params: match.params,
@@ -205,7 +220,8 @@ export async function startObserveDaemon(options: ObserveDaemonOptions = {}): Pr
   const pidPath = options.pidPath;
   if (pidPath !== undefined) {
     fs.mkdirSync(path.dirname(pidPath), { recursive: true });
-    fs.writeFileSync(pidPath, String(process.pid), 'utf8');
+    // Line 2 is the port, so `stop` can ask this daemon which db it serves.
+    fs.writeFileSync(pidPath, `${process.pid}\n${boundPort}\n`, 'utf8');
   }
 
   // The monitoring sweep: rewrites agents.status from heartbeat freshness,
@@ -250,6 +266,8 @@ export interface HealthProbe {
   service: string;
   ok: boolean;
   version?: string;
+  /** Absolute path of the db the daemon serves. */
+  db?: string;
 }
 
 /**
diff --git a/src/observe/routes/httpKit.ts b/src/observe/routes/httpKit.ts
index e598fb70..d76dc0ff 100644
--- a/src/observe/routes/httpKit.ts
+++ b/src/observe/routes/httpKit.ts
@@ -17,6 +17,8 @@ export { sendJson };
 /** What a handler gets: the request, the matched `:params`, the query, the db, and a bounded body reader. */
 export interface RouteContext {
   db: SqlDatabase;
+  /** The db file path the daemon was started with (`:memory:` for tests). */
+  dbPath: string;
   req: http.IncomingMessage;
   res: http.ServerResponse;
   params: Record<string, string>;
diff --git a/src/observe/routes/scores.test.ts b/src/observe/routes/scores.test.ts
index 4079d535..5fb003a8 100644
--- a/src/observe/routes/scores.test.ts
+++ b/src/observe/routes/scores.test.ts
@@ -45,6 +45,7 @@ function get(database: SqlDatabase, query: string): Captured {
   if (!matched) throw new Error('scores route not registered');
   matched.route.handle({
     db: database,
+    dbPath: ':memory:',
     req: {} as http.IncomingMessage,
     res,
     params: matched.params,
diff --git a/src/observe/routes/status.ts b/src/observe/routes/status.ts
index 0195d801..32a84df8 100644
--- a/src/observe/routes/status.ts
+++ b/src/observe/routes/status.ts
@@ -6,6 +6,7 @@
  * row-count surface `lousho observe status` prints.
  */
 
+import * as path from 'node:path';
 import { VERSION } from '../../version';
 import { observeCounts } from '../store';
 import { sendJson, type Route } from './httpKit';
@@ -14,8 +15,9 @@ export const statusRoutes: readonly Route[] = [
   {
     method: 'GET',
     path: '/health',
-    handle: ({ res }) => {
-      sendJson(res, 200, { service: 'lousho-observe', ok: true, version: VERSION });
+    handle: ({ res, dbPath }) => {
+      // `db` lets `start`/`stop` tell which database a port or pid serves.
+      sendJson(res, 200, { service: 'lousho-observe', ok: true, version: VERSION, db: dbPath === ':memory:' ? dbPath : path.resolve(dbPath) });
     },
   },
   {