diff --git a/decnet/web/db/sqlmodel_repo/__init__.py b/decnet/web/db/sqlmodel_repo/__init__.py
index 9bdc7bf5..c7708067 100644
--- a/decnet/web/db/sqlmodel_repo/__init__.py
+++ b/decnet/web/db/sqlmodel_repo/__init__.py
@@ -12,7 +12,6 @@ backends.  Dialect-specific behavior lives in subclasses:
 """
 from __future__ import annotations
 
-import asyncio
 import json
 import os
 
@@ -23,7 +22,6 @@ from typing import Any, Optional, List, cast
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker
 
-from decnet.config import load_state
 from decnet.env import DECNET_ADMIN_USER, DECNET_ADMIN_PASSWORD
 from decnet.web.auth import get_password_hash
 from decnet.web.db.repository import BaseRepository
@@ -172,8 +170,14 @@ class SQLModelRepository(
         return None
 
     async def get_deckies(self) -> List[dict]:
-        _state = await asyncio.to_thread(load_state)
-        return [_d.model_dump() for _d in _state[0].deckies] if _state else []
+        # The fleet inventory the UI/API sees is fleet_deckies — the
+        # engine-mirrored table written on EVERY deploy/teardown (CLI or web),
+        # per the source-of-truth model documented in fleet/reconciler.py.
+        # Each row's decky_config column is a full DeckyConfig.model_dump(
+        # mode="json"), so it rehydrates to the same shape load_state() used
+        # to return. See development/ADR-001-FLEET-SOURCE-OF-TRUTH.md.
+        rows = await self.list_fleet_deckies()
+        return [r["decky_config"] for r in rows if r.get("decky_config")]
 
     # --------------------------------------------------------------- users
 
diff --git a/decnet/web/router/fleet/api_deploy_deckies.py b/decnet/web/router/fleet/api_deploy_deckies.py
index 0aaca351..9da9180f 100644
--- a/decnet/web/router/fleet/api_deploy_deckies.py
+++ b/decnet/web/router/fleet/api_deploy_deckies.py
@@ -8,7 +8,7 @@ from decnet.bus.factory import get_bus
 from decnet.lifecycle.runner import run_deploy
 from decnet.logging import get_logger
 from decnet.telemetry import traced as _traced
-from decnet.config import DEFAULT_MUTATE_INTERVAL, DecnetConfig, _ROOT
+from decnet.config import DEFAULT_MUTATE_INTERVAL, DecnetConfig, DeckyConfig, _ROOT
 from decnet.ini_loader import load_ini_from_string
 from decnet.network import detect_interface, detect_subnet, get_host_ip
 from decnet.web.dependencies import require_admin, repo
@@ -19,6 +19,39 @@ log = get_logger("api")
 router = APIRouter()
 
 
+async def _commit_fleet_to_db(deckies: list[DeckyConfig], *, replace_fleet: bool) -> None:
+    """Synchronously reconcile ``fleet_deckies`` to *deckies*.
+
+    fleet_deckies is the source of truth the deploy guard now reads
+    (``existing_deckies``). Committing the intended shape here — before the
+    async deploy task's engine mirror runs — means rapid sequential web
+    deploys each read a current fleet (no self-wipe) and the dashboard
+    observes the new shape immediately. Mirrors the payload shape of
+    ``engine.deployer._mirror_fleet_deploy_to_db``.
+
+    In replace mode, rows absent from *deckies* are deleted so the committed
+    inventory matches the desired set; the async reconciler/teardown mirror
+    converges the actual containers separately.
+    """
+    from decnet.web.db.models import LOCAL_HOST_SENTINEL
+
+    keep = {(d.host_uuid or LOCAL_HOST_SENTINEL, d.name) for d in deckies}
+    if replace_fleet:
+        for row in await repo.list_fleet_deckies():
+            host = row.get("host_uuid") or LOCAL_HOST_SENTINEL
+            if (host, row.get("name")) not in keep:
+                await repo.delete_fleet_decky(host_uuid=host, name=row["name"])
+    for d in deckies:
+        await repo.upsert_fleet_decky({
+            "host_uuid": d.host_uuid or LOCAL_HOST_SENTINEL,
+            "name": d.name,
+            "services": list(d.services),
+            "decky_config": d.model_dump(mode="json"),
+            "decky_ip": d.ip,
+            "state": "running",
+        })
+
+
 @router.post(
     "/deckies/deploy",
     tags=["Fleet Management"],
@@ -81,7 +114,19 @@ async def api_deploy_deckies(req: DeployIniRequest, admin: dict = Depends(requir
     # config below) so additive collision checks compare new against prior
     # rather than against themselves. Existing IPs are passed into
     # build_deckies_from_ini as reserved so auto-allocation skips them.
-    existing_deckies = list(config.deckies) if config is not None else []
+    # The existing fleet comes from fleet_deckies (engine-mirrored on CLI
+    # *and* web deploys), NOT from config.deckies carried by the
+    # State["deployment"] key. A CLI/seed-established fleet never lands in
+    # that key, so the additive collision guard ran blind and the reconciler
+    # wiped the fleet — root cause of BUG-2. fleet_deckies is the store the
+    # source-of-truth model (fleet/reconciler.py) names as the API's view.
+    # See development/ADR-001-FLEET-SOURCE-OF-TRUTH.md.
+    existing_rows = await repo.list_fleet_deckies()
+    existing_deckies = [
+        DeckyConfig(**r["decky_config"])
+        for r in existing_rows
+        if r.get("decky_config")
+    ]
     reserved_ips: set[str] | None = (
         {d.ip for d in existing_deckies if d.ip}
         if not req.replace_fleet and existing_deckies
@@ -192,6 +237,11 @@ async def api_deploy_deckies(req: DeployIniRequest, admin: dict = Depends(requir
         ),
     }
     await repo.set_state("deployment", new_state_payload)
+    # Commit the intended fleet to fleet_deckies — the store the deploy guard
+    # and get_deckies() now read. set_state("deployment") above is retained
+    # for the mutate handlers / mutator engine that still coordinate through
+    # that key (their consolidation is tracked in the ADR, open question 7).
+    await _commit_fleet_to_db(config.deckies, replace_fleet=req.replace_fleet)
 
     # Lifecycle rows track THIS call's deployments only. In additive mode
     # the existing deckies are already running and don't get a new
diff --git a/development/ADR-001-FLEET-SOURCE-OF-TRUTH.md b/development/ADR-001-FLEET-SOURCE-OF-TRUTH.md
new file mode 100644
index 00000000..1be9cf05
--- /dev/null
+++ b/development/ADR-001-FLEET-SOURCE-OF-TRUTH.md
@@ -0,0 +1,177 @@
+# ADR-001 — Fleet Source of Truth
+
+- **Status:** PROPOSED (discussion — not yet accepted)
+- **Date:** 2026-06-12
+- **Context owner:** ANTI
+- **Drives fix for:** BUG-2 (destructive fleet-replace / silent wipe), see `QA_REPORT.md`
+
+---
+
+## 1. Context
+
+DECNET currently keeps the deployed-fleet inventory in **two unsynchronized stores**:
+
+| Store | Read by | Written by |
+|-------|---------|------------|
+| `decnet-state.json` file (`load_state()`) | `repo.get_deckies()` → the UI fleet view, collision pre-checks | CLI/engine path (`engine.deployer.save_state`), `decnet status`, sniffer, collector |
+| DB `State` table, key `"deployment"` (`repo.get_state`/`set_state`) | the web deploy handler's `existing_deckies` snapshot | **only** the web deploy handler |
+
+The web is a **non-dependency**: the same deploys can be driven entirely from the CLI, and CLI state lives in `decnet-state.json`. Because the two stores never reconcile, a fleet established via CLI/seed is invisible to the web deploy handler's collision guard.
+
+### BUG-2 failure chain (source-traced)
+
+1. CLI/seed establishes a fleet → written to `decnet-state.json`, **never** to DB `"deployment"`.
+2. UI reads `get_deckies()` (JSON) → shows decky-02/03 correctly.
+3. Wizard POSTs a new decky-04 with `replace_fleet=false`.
+4. Handler reads `existing_deckies` from `repo.get_state("deployment")` → **None** → `existing_deckies = []`.
+5. Collision guard compares against `[]` → no conflict → `config.deckies = [] + [decky-04]`.
+6. `run_deploy` → `LocalDeployStrategy` → `engine.deployer.deploy(config)`:
+   - `write_compose(config, COMPOSE_FILE)` writes a compose file containing **only decky-04** (`deployer.py:681`).
+   - `_compose("down", "--remove-orphans", …)` (`deployer.py:708`) tears down the whole compose project, then `up` brings back only decky-04.
+   - `_mirror_fleet_teardown_to_db` drops the survivors' rows.
+7. Result: fleet silently wiped to one decky. HTTP 202. No warning.
+
+**Key trap:** the destructive call is `deployer.py:708` (`down --remove-orphans` against a compose file rewritten from `config.deckies`). Any source-of-truth fix that does not also guarantee `config.deckies` is the **complete** desired fleet before `write_compose` leaves BUG-2 alive.
+
+---
+
+## 2. What the UI actually consumes
+
+`DeckyConfig` (`decnet/models.py:87`) full field set:
+
+```
+name, ip, services[], distro, base_image, build_base, hostname,
+archetype, service_config{}, nmap_os, mutate_interval, last_mutated,
+last_login_attempt, host_uuid
+```
+
+Frontend `Decky` type (`DeckyFleet/types.ts`) + what is **rendered/edited**:
+
+| Field | Displayed? | Where |
+|-------|-----------|-------|
+| name, ip, services | yes | DeckyCard / InspectPanel |
+| hostname, distro, archetype | yes | DeckyInspectPanel:77-79 |
+| mutate_interval, last_mutated | yes | DeckyInspectPanel:80-81 |
+| **service_config** | **yes — EDITED** | DeckyCard:322 (per-service config editor `currentConfig`) |
+| base_image, build_base, nmap_os, last_login_attempt | no | — |
+
+**Conclusion:** `service_config` is not just stored — it is rendered and **edited** in the UI. A "minimal scalar labels" scheme (name/ip/services only) would amputate editable state. Fidelity requires carrying the full `DeckyConfig`.
+
+---
+
+## 3. Options
+
+### Option A — API reads only the DB; ignore `decnet-state.json` (web side)
+
+Align `get_deckies()` and the deploy handler both on DB `"deployment"`. The web becomes a self-contained plane on the DB; CLI stays on the JSON file. The two planes are explicitly **non-interoperable**.
+
+- **Pros:** smallest change; closes the desync *within the web plane*.
+- **Cons:** ANTI's own verdict — "honestly the incorrect way of doing things." Two planes that can't see each other is a design smell, not a fix. A CLI-seeded fleet is still invisible to the web (and vice-versa); the wizard would still drive a reconciler that tears down CLI containers it can't see. Does **not** fix the cross-plane wipe, only the intra-web one.
+
+### Option B — Docker container labels as source of truth (ANTI's proposal)
+
+Stamp every DECNET container with provenance + identity labels; reconstruct the fleet by querying Docker. `decnet-state.json` degrades to a CLI-side convenience cache, no longer authoritative.
+
+Proposed labels:
+```
+com.decnet.host        = "true"          # selector for "this is a DECNET decky"
+com.decnet.deploy_type = "api" | "cli"   # provenance, NOT a partition
+com.decnet.service     = "<service>"     # or the broader identity
+com.decnet.config      = "<DeckyConfig JSON>"  # REQUIRED to preserve service_config fidelity (see §2)
+```
+
+Fleet read becomes `docker ps --filter label=com.decnet.host=true` (+ `-a` for stopped), then deserialize `com.decnet.config`.
+
+- **Pros:**
+  - **One source of truth = reality.** The collision guard and the reconciler read the SAME state, so BUG-2 cannot recur.
+  - Survives a DECNET process restart (Docker keeps running; labels persist on the real object).
+  - `deploy_type` makes the "two planes" distinction unnecessary — one fleet, labeled by origin. The guard queries ALL `com.decnet.host=true` regardless of origin, so it can never blind-wipe a CLI decky.
+  - This is the orchestrator-standard pattern (label the real object, reconcile against it).
+- **Cons / constraints:**
+  - **Swarm.** The master cannot `docker ps` a remote worker. Remote deckies STILL need a registry → keep `decky_shards` (DB, heartbeat-driven). Honest model is **hybrid**: local truth = labels, remote truth = `decky_shards`.
+  - **Fleet-global config** (`interface, subnet, gateway, ipvlan, mutate_interval, log_file, compose_path`) is not per-container. Proposed home: **labels on the macvlan/ipvlan network object** (exactly one, DECNET-owned, correct scope). NOT replicated onto every container.
+  - **Label payload.** Preserving `service_config` fidelity forces a `com.decnet.config` JSON blob. Works (label values are generous) but it is config-in-label-land, with its own serialization discipline.
+  - **Performance.** `/deckies` is UI-polled and load-tested. Querying Docker on every read is heavier than a file/DB read. Mitigation: the existing 5s TTL cache (`api_get_deckies.py:_DECKIES_TTL`) extends naturally over the Docker query.
+  - **Does NOT by itself fix `deployer.py:708`.** Labels give the DATA to build the COMPLETE config (live + new) before `write_compose`; the merge must actually be done. Labels make the correct merge possible; they don't perform it.
+
+### Option C — Single DB store as canonical (both web and CLI write DB)
+
+Make the CLI write the DB `"deployment"` key too; retire `decnet-state.json` as authority. One store, but it's bookkeeping, not reality — can still drift from actual containers on crash/manual `docker rm`.
+
+- **Pros:** single store; no Docker-query perf cost; swarm-friendly (DB is already the remote registry).
+- **Cons:** reintroduces the "trust the ledger, not reality" fragility that Option B specifically escapes; CLI now hard-depends on the DB being reachable, eroding the web-is-a-non-dependency property.
+
+---
+
+## 4. Recommendation (for discussion)
+
+**Option B (labels), accepted as a hybrid:** local fleet truth = Docker labels; remote fleet truth = `decky_shards` (DB); fleet-global config = network-object labels; `decnet-state.json` demoted to CLI convenience cache.
+
+Mandatory companion change regardless of option chosen: **build the complete desired `config.deckies` (surviving live fleet + new submissions) before `write_compose`/`deployer.py:708`**, so `down --remove-orphans` + `up` is a no-op on survivors. This is the actual teardown fix; the source-of-truth choice only determines *where the survivor list is read from*.
+
+---
+
+## 5. Open questions (resolve before cutting code)
+
+1. **`com.decnet.config` blob vs. exploded scalar labels** — do we accept one JSON label for fidelity, or split into N labels and reconstruct? (Fidelity for `service_config` pushes toward the blob.)
+2. **Global config home** — network-object labels confirmed as the home, or a single sentinel "fleet" container/label set?
+3. **Swarm boundary** — is the local-labels / remote-`decky_shards` split acceptable, or do we want labels mirrored back to the master via heartbeat for a uniform read path?
+4. **Stopped/failed containers** — does `-a` (include stopped) count toward the fleet for collision purposes, and how do we represent non-running status the JSON file never tracked?
+5. **Migration** — first label-aware deploy after upgrade: how do we adopt already-running unlabeled containers (relabel in place vs. require one redeploy)?
+6. **`decnet-state.json` final role** — pure CLI cache, or removed entirely with CLI also reading labels?
+
+---
+
+## 6. Affected files (for whichever option lands)
+
+- `decnet/web/router/fleet/api_deploy_deckies.py` — `existing_deckies` snapshot (lines 48, 84), collision guard (124-145), `set_state("deployment")` (194)
+- `decnet/web/router/fleet/api_get_deckies.py` — `get_deckies` read path + TTL cache
+- `decnet/web/db/sqlmodel_repo/__init__.py:174` — `get_deckies()` (currently `load_state()`)
+- `decnet/engine/deployer.py:681` (`write_compose`), `:708` (`down --remove-orphans`), `:571`/`:623` (`_mirror_fleet_*`)
+- `decnet/config.py` — `save_state`/`load_state`, `STATE_FILE`
+- `decnet/lifecycle/runner.py` / `strategies.py` — `LocalDeployStrategy` → `deployer.deploy`
+- `decnet/models.py:87` — `DeckyConfig` (label serialization surface)
+
+---
+
+## 7. CORRECTION (source-traced 2026-06-12) — the store topology is wider than §1 said
+
+§1's claim that DB `State["deployment"]` is *"written only by the web deploy handler"* is **WRONG**. A grep for its readers/writers shows it is the shared coordination store for the **entire web + mutator plane**:
+
+| Site | Op |
+|------|----|
+| `api_deploy_deckies.py:48,194` | read + write |
+| `api_mutate_decky.py:55,76` | read + write |
+| `api_mutate_interval.py:32,45` | read + write |
+| `swarm_mgmt/api_list_deckies.py:28` | read |
+| `mutator/engine.py:84,126,189,413` | read + write (autonomous mutator) |
+
+Consequences:
+- A one-line "deploy handler reads `load_state()`" swap makes deploy **diverge from its own plane** (mutate handlers + the background mutator still read the DB key). Lateral move, not a fix. **Empirically confirmed:** that edit broke 4/5 tests in `tests/api/fleet/test_deploy_additive.py` (the survivor was `replace_fleet=True`, the only case that doesn't read the prior fleet), because under `DECNET_CONTRACT_TEST` the deploy task is skipped so `save_state` never writes the JSON, and the handler couldn't see its own prior `set_state` write. Read-one-store / write-another is self-inconsistent.
+- Pointing `get_deckies()` at the DB key **also fails to fix BUG-2**: a CLI-seeded fleet isn't in `State["deployment"]` either (CLI writes JSON + `fleet_deckies`), so the reconcile-against-incomplete-inventory wipe survives.
+
+### The model the codebase ALREADY documents (`fleet/reconciler.py:1-29`)
+
+```
+1. decnet-state.json — canonical for offline / no-API consumers (CLI, status, sniffer, collector)
+2. fleet_deckies table — "what the orchestrator, web dashboard, and REST API see"
+3. docker inspect — actual per-container runtime state
+Resolution: JSON-only → INSERT; DB-only(this host) → DELETE; both → state := docker-aggregated.
+```
+
+Two facts this hands us:
+1. **The API was DESIGNED to read `fleet_deckies`** — the engine-mirrored table written on *every* deploy/teardown regardless of origin (`deployer.py:571 _mirror_fleet_deploy_to_db`, `:623` teardown). The live deploy/collision-guard code reading `State["deployment"]`, and `get_deckies()` reading the JSON file, are both **drift from the documented design**. `fleet_deckies` is the cross-plane store that *does* contain a CLI-seeded fleet.
+2. **Docker is already the ultimate authority** — the reconciler converges JSON and DB *to docker-aggregated state*. ANTI's label proposal (Option B) is not a new paradigm; it promotes docker from reconciler-tiebreaker to primary read path.
+
+### Revised recommendation
+
+Two viable directions, both grounded in the existing design rather than a new store:
+
+- **B′ (labels / docker-primary)** — the ADR's Option B, now understood as *promoting* the reconciler's existing docker-authoritative tiebreaker to the primary fleet read. Strongest long-term; same swarm caveat (remote = `decky_shards`/`fleet_deckies`, master can't `docker ps` workers).
+- **D (converge on `fleet_deckies` now)** — make the deploy collision-guard AND `get_deckies()` read `fleet_deckies` (`list_fleet_deckies` / `list_running_fleet_deckies`), the store the design already names as the API's view. Smaller than relabelling; immediately closes the CLI-invisible-to-web gap because `fleet_deckies` is engine-mirrored on CLI deploys too. The mutate handlers + mutator engine reading `State["deployment"]` become the next consolidation target.
+
+**Unchanged hard constraint:** whichever store wins, the handler must still build the COMPLETE desired `config.deckies` (survivors + new) before `write_compose`/`deployer.py:708`. The store choice only decides where "survivors" is read from.
+
+### Open question added to §5
+
+7. **`State["deployment"]` vs `fleet_deckies`** — do we converge the whole web+mutator plane onto `fleet_deckies` (Option D), or go straight to docker-primary (Option B′) and let `fleet_deckies` be the swarm/remote registry? The mutator engine (`mutator/engine.py`) is the heaviest consumer of `State["deployment"]` and must move in lockstep.
diff --git a/tests/api/config/test_deploy_limit.py b/tests/api/config/test_deploy_limit.py
index 0fcd949e..9b5a82ab 100644
--- a/tests/api/config/test_deploy_limit.py
+++ b/tests/api/config/test_deploy_limit.py
@@ -2,6 +2,8 @@
 import pytest
 from unittest.mock import patch
 
+from decnet.config import DeckyConfig
+from decnet.web.db.models import LOCAL_HOST_SENTINEL
 from decnet.web.dependencies import repo
 
 
@@ -15,70 +17,93 @@ def contract_test_mode(monkeypatch):
 def mock_network():
     """Mock network detection so deploy doesn't call `ip addr show`."""
     with patch("decnet.web.router.fleet.api_deploy_deckies.get_host_ip", return_value="192.168.1.100"):
-        yield
+        with patch("decnet.web.router.fleet.api_deploy_deckies.detect_interface", return_value="eth0"):
+            with patch("decnet.web.router.fleet.api_deploy_deckies.detect_subnet", return_value=("192.168.1.0/24", "192.168.1.1")):
+                yield
+
+
+async def _clear_fleet() -> None:
+    for row in await repo.list_fleet_deckies():
+        await repo.delete_fleet_decky(
+            host_uuid=row.get("host_uuid") or LOCAL_HOST_SENTINEL,
+            name=row["name"],
+        )
+
+
+async def _seed_fleet(name: str, ip: str) -> None:
+    cfg = DeckyConfig(
+        name=name, ip=ip, services=["ssh"], distro="debian",
+        base_image="debian", hostname=name,
+    )
+    await repo.upsert_fleet_decky({
+        "host_uuid": LOCAL_HOST_SENTINEL,
+        "name": name,
+        "services": ["ssh"],
+        "decky_config": cfg.model_dump(mode="json"),
+        "decky_ip": ip,
+        "state": "running",
+    })
+
+
+@pytest.fixture(autouse=True)
+async def _isolate_fleet():
+    await _clear_fleet()
+    yield
+    await _clear_fleet()
 
 
 @pytest.mark.anyio
-async def test_deploy_respects_limit(client, auth_token, mock_state_file):
-    """Deploy should reject if the *submitted* INI exceeds the limit.
-    The INI is the source of truth — prior state is fully replaced — so the
-    check runs on the new decky count alone."""
+async def test_deploy_respects_limit(client, auth_token):
+    """The limit counts the WHOLE resulting fleet — existing (from
+    fleet_deckies) plus the submitted INI — not the INI alone. One existing
+    decky + one submitted, against a limit of 1, must be rejected."""
     await repo.set_state("config_limits", {"deployment_limit": 1})
-    await repo.set_state("deployment", mock_state_file)
+    await _seed_fleet("decky-existing", "192.168.1.10")
 
-    ini = """[decky-a]
-services = ssh
-
-[decky-b]
-services = ssh
-"""
+    ini = "[decky-new]\nservices = ssh\n"
     resp = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": ini},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    # 2 new deckies > limit of 1
+    # existing(1) + new(1) = 2 > limit 1
     assert resp.status_code == 409
     assert "limit" in resp.json()["detail"].lower()
 
 
 @pytest.mark.anyio
-async def test_deploy_replaces_prior_state(client, auth_token, mock_state_file):
-    """Submitting an INI with 1 decky must not silently re-include the 2
-    deckies from prior state (that caused the 'Address already in use'
-    regression when stale decky2/decky3 redeployed on stale IPs)."""
+async def test_deploy_replaces_prior_state(client, auth_token):
+    """replace_fleet=True drops the prior fleet rather than silently
+    re-including it (the 'Address already in use' regression came from stale
+    deckies redeploying on stale IPs). After replace, the committed fleet is
+    exactly the submitted INI."""
     await repo.set_state("config_limits", {"deployment_limit": 10})
-    await repo.set_state("deployment", mock_state_file)
+    await _seed_fleet("test-decky-1", "192.168.1.10")
+    await _seed_fleet("test-decky-2", "192.168.1.11")
 
-    ini = """[only-decky]
-services = ssh
-"""
+    ini = "[only-decky]\nservices = ssh\n"
     resp = await client.post(
         "/api/v1/deckies/deploy",
-        json={"ini_content": ini},
+        json={"ini_content": ini, "replace_fleet": True},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert resp.status_code == 202
-    persisted = await repo.get_state("deployment")
-    names = [d["name"] for d in persisted["config"]["deckies"]]
-    assert names == ["only-decky"]
+    assert resp.status_code == 202, resp.text
+    names = {d["name"] for d in await repo.get_deckies()}
+    assert names == {"only-decky"}
 
 
 @pytest.mark.anyio
-async def test_deploy_within_limit(client, auth_token, mock_state_file):
-    """Deploy should succeed when within limit."""
+async def test_deploy_within_limit(client, auth_token):
+    """Deploy should succeed when the resulting fleet is within limit."""
     await repo.set_state("config_limits", {"deployment_limit": 100})
-    await repo.set_state("deployment", mock_state_file)
+    await _seed_fleet("decky-existing", "192.168.1.10")
 
-    ini = """[decky-new]
-services = ssh
-"""
+    ini = "[decky-new]\nservices = ssh\n"
     resp = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": ini},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    # Should not fail due to limit
     if resp.status_code == 409:
         assert "limit" not in resp.json()["detail"].lower()
     else:
diff --git a/tests/api/conftest.py b/tests/api/conftest.py
index 9c512c19..edb4378c 100644
--- a/tests/api/conftest.py
+++ b/tests/api/conftest.py
@@ -211,6 +211,47 @@ def mock_state_file(patch_state_file: Path):
     patch_state_file.write_text(json.dumps(_test_state))
     yield _test_state
 
+
+@pytest.fixture
+async def mock_fleet_deckies():
+    """Seed fleet_deckies with two deckies — the store get_deckies() reads
+    under the Option-D source-of-truth model (development/ADR-001-...md).
+    Mirrors the data mock_state_file used to put in decnet-state.json."""
+    from decnet.config import DeckyConfig
+    from decnet.web.db.models import LOCAL_HOST_SENTINEL
+    from decnet.web.dependencies import repo
+
+    async def _clear() -> None:
+        for row in await repo.list_fleet_deckies():
+            await repo.delete_fleet_decky(
+                host_uuid=row.get("host_uuid") or LOCAL_HOST_SENTINEL,
+                name=row["name"],
+            )
+
+    specs = [
+        ("test-decky-1", "192.168.1.10", ["ssh"], "debian", "test-host-1",
+         {"ssh": {"banner": "SSH-2.0-OpenSSH_8.9"}}, "deaddeck"),
+        ("test-decky-2", "192.168.1.11", ["http"], "ubuntu", "test-host-2",
+         {}, None),
+    ]
+    await _clear()
+    for name, ip, services, distro, hostname, svc_cfg, arche in specs:
+        cfg = DeckyConfig(
+            name=name, ip=ip, services=services, distro=distro,
+            base_image=distro, hostname=hostname,
+            service_config=svc_cfg, archetype=arche,
+        )
+        await repo.upsert_fleet_decky({
+            "host_uuid": LOCAL_HOST_SENTINEL,
+            "name": name,
+            "services": services,
+            "decky_config": cfg.model_dump(mode="json"),
+            "decky_ip": ip,
+            "state": "running",
+        })
+    yield
+    await _clear()
+
 # Share fuzz settings across API tests
 # FUZZ_EXAMPLES: keep low for dev speed; bump via HYPOTHESIS_MAX_EXAMPLES env var in CI
 _FUZZ_EXAMPLES = int(_os.environ.get("HYPOTHESIS_MAX_EXAMPLES", "10"))
diff --git a/tests/api/fleet/test_deploy_additive.py b/tests/api/fleet/test_deploy_additive.py
index cd025fb1..97a582dc 100644
--- a/tests/api/fleet/test_deploy_additive.py
+++ b/tests/api/fleet/test_deploy_additive.py
@@ -5,6 +5,13 @@ Default behaviour (replace_fleet=False) appends the INI to the existing
 fleet so the wizard's "deploy one more decky" submit no longer wipes
 prior deckies. replace_fleet=True preserves the historical
 set-desired-state semantics for CLI / declarative callers.
+
+The existing fleet is read from fleet_deckies — the engine-mirrored table
+written on every deploy/teardown (CLI or web), per the source-of-truth
+model in fleet/reconciler.py. These tests seed fleet_deckies directly,
+which also models the BUG-2 scenario: a fleet established out of band
+(CLI/seed) that the web deploy guard must see and append to rather than
+wipe. See development/ADR-001-FLEET-SOURCE-OF-TRUTH.md.
 """
 from __future__ import annotations
 
@@ -12,6 +19,8 @@ from unittest.mock import patch
 
 import pytest
 
+from decnet.config import DeckyConfig
+from decnet.web.db.models import LOCAL_HOST_SENTINEL
 from decnet.web.dependencies import repo
 
 
@@ -28,96 +37,111 @@ def mock_network():
                 yield
 
 
+async def _clear_fleet() -> None:
+    for row in await repo.list_fleet_deckies():
+        await repo.delete_fleet_decky(
+            host_uuid=row.get("host_uuid") or LOCAL_HOST_SENTINEL,
+            name=row["name"],
+        )
+
+
+async def _seed_fleet(name: str, *, ip: str = "192.168.1.10", services=("ssh",)) -> None:
+    """Insert a decky into fleet_deckies, as the engine mirror does on a
+    CLI/web deploy. Stamps a full DeckyConfig into decky_config so the deploy
+    guard can rehydrate it."""
+    cfg = DeckyConfig(
+        name=name,
+        ip=ip,
+        services=list(services),
+        distro="debian",
+        base_image="debian:bookworm-slim",
+        hostname=name,
+    )
+    await repo.upsert_fleet_decky({
+        "host_uuid": LOCAL_HOST_SENTINEL,
+        "name": name,
+        "services": list(services),
+        "decky_config": cfg.model_dump(mode="json"),
+        "decky_ip": ip,
+        "state": "running",
+    })
+
+
 @pytest.fixture(autouse=True)
 async def _isolate_state():
     for row in await repo.list_swarm_hosts():
         await repo.delete_swarm_host(row["uuid"])
     await repo.set_state("deployment", None)
+    await _clear_fleet()
     yield
     await repo.set_state("deployment", None)
+    await _clear_fleet()
 
 
 @pytest.mark.anyio
-async def test_additive_default_appends_to_existing_fleet(client, auth_token, monkeypatch):
-    """Two sequential deploys with replace_fleet unset → both deckies in state."""
+async def test_additive_onto_existing_fleet_appends_not_wipes(client, auth_token, monkeypatch):
+    """BUG-2 regression: an additive web deploy onto a fleet established out
+    of band (CLI/seed → fleet_deckies) appends rather than wiping it.
+
+    Previously the guard read State["deployment"] (empty for a CLI-seeded
+    fleet), so existing_deckies was [] and the reconciler tore the running
+    fleet down to the single submitted decky."""
     monkeypatch.setenv("DECNET_MODE", "master")
+    await _seed_fleet("decky-01", ip="192.168.1.10")
 
-    r1 = await client.post(
-        "/api/v1/deckies/deploy",
-        json={"ini_content": "[decky-01]\nservices = ssh\n"},
-        headers={"Authorization": f"Bearer {auth_token}"},
-    )
-    assert r1.status_code == 202, r1.text
-
-    r2 = await client.post(
+    r = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": "[decky-02]\nservices = http\n"},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert r2.status_code == 202, r2.text
+    assert r.status_code == 202, r.text
 
-    committed = await repo.get_state("deployment")
-    assert committed is not None
-    names = {d["name"] for d in committed["config"]["deckies"]}
+    names = {d["name"] for d in await repo.get_deckies()}
     assert names == {"decky-01", "decky-02"}
 
 
 @pytest.mark.anyio
 async def test_additive_name_collision_returns_409(client, auth_token, monkeypatch):
-    """Re-submitting an existing decky name without replace_fleet → 409."""
+    """Submitting a decky whose name already exists in the fleet without
+    replace_fleet → 409."""
     monkeypatch.setenv("DECNET_MODE", "master")
+    await _seed_fleet("decky-01")
 
-    r1 = await client.post(
-        "/api/v1/deckies/deploy",
-        json={"ini_content": "[decky-01]\nservices = ssh\n"},
-        headers={"Authorization": f"Bearer {auth_token}"},
-    )
-    assert r1.status_code == 202, r1.text
-
-    r2 = await client.post(
+    r = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": "[decky-01]\nservices = http\n"},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert r2.status_code == 409, r2.text
-    assert "decky-01" in r2.json()["detail"]
-    assert "replace_fleet" in r2.json()["detail"]
+    assert r.status_code == 409, r.text
+    assert "decky-01" in r.json()["detail"]
+    assert "replace_fleet" in r.json()["detail"]
 
 
 @pytest.mark.anyio
 async def test_additive_ip_collision_returns_409(client, auth_token, monkeypatch):
-    """A new decky pinned to an IP already in use → 409 with the IP."""
+    """A new decky pinned to an IP already in use by the existing fleet → 409
+    with the IP."""
     monkeypatch.setenv("DECNET_MODE", "master")
+    await _seed_fleet("decky-01", ip="192.168.1.50")
 
-    r1 = await client.post(
-        "/api/v1/deckies/deploy",
-        json={"ini_content": "[decky-01]\nservices = ssh\nip = 192.168.1.50\n"},
-        headers={"Authorization": f"Bearer {auth_token}"},
-    )
-    assert r1.status_code == 202, r1.text
-
-    r2 = await client.post(
+    r = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": "[decky-02]\nservices = http\nip = 192.168.1.50\n"},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert r2.status_code == 409, r2.text
-    assert "192.168.1.50" in r2.json()["detail"]
+    assert r.status_code == 409, r.text
+    assert "192.168.1.50" in r.json()["detail"]
 
 
 @pytest.mark.anyio
 async def test_replace_fleet_true_overwrites_existing(client, auth_token, monkeypatch):
-    """replace_fleet=True preserves the historical full-replace semantics."""
+    """replace_fleet=True preserves the historical full-replace semantics:
+    the existing fleet is dropped and the committed inventory is exactly the
+    submitted INI."""
     monkeypatch.setenv("DECNET_MODE", "master")
+    await _seed_fleet("decky-01")
 
-    r1 = await client.post(
-        "/api/v1/deckies/deploy",
-        json={"ini_content": "[decky-01]\nservices = ssh\n"},
-        headers={"Authorization": f"Bearer {auth_token}"},
-    )
-    assert r1.status_code == 202, r1.text
-
-    r2 = await client.post(
+    r = await client.post(
         "/api/v1/deckies/deploy",
         json={
             "ini_content": "[decky-02]\nservices = http\n",
@@ -125,11 +149,9 @@ async def test_replace_fleet_true_overwrites_existing(client, auth_token, monkey
         },
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert r2.status_code == 202, r2.text
+    assert r.status_code == 202, r.text
 
-    committed = await repo.get_state("deployment")
-    assert committed is not None
-    names = {d["name"] for d in committed["config"]["deckies"]}
+    names = {d["name"] for d in await repo.get_deckies()}
     assert names == {"decky-02"}
 
 
@@ -139,25 +161,16 @@ async def test_additive_lifecycle_ids_scoped_to_new_deckies(client, auth_token,
     the caller submitted, not carryover. Operators polling
     /deckies/lifecycle?ids=... see exactly what this call deployed."""
     monkeypatch.setenv("DECNET_MODE", "master")
+    await _seed_fleet("decky-01", ip="192.168.1.10")
+    await _seed_fleet("decky-02", ip="192.168.1.11")
 
-    r1 = await client.post(
-        "/api/v1/deckies/deploy",
-        json={"ini_content": "[decky-01]\nservices = ssh\n[decky-02]\nservices = http\n"},
-        headers={"Authorization": f"Bearer {auth_token}"},
-    )
-    assert r1.status_code == 202, r1.text
-    assert len(r1.json()["lifecycle_ids"]) == 2
-
-    r2 = await client.post(
+    r = await client.post(
         "/api/v1/deckies/deploy",
         json={"ini_content": "[decky-03]\nservices = ssh\n"},
         headers={"Authorization": f"Bearer {auth_token}"},
     )
-    assert r2.status_code == 202, r2.text
-    body2 = r2.json()
-    assert len(body2["lifecycle_ids"]) == 1
+    assert r.status_code == 202, r.text
+    assert len(r.json()["lifecycle_ids"]) == 1
 
-    committed = await repo.get_state("deployment")
-    assert committed is not None
-    names = {d["name"] for d in committed["config"]["deckies"]}
+    names = {d["name"] for d in await repo.get_deckies()}
     assert names == {"decky-01", "decky-02", "decky-03"}
diff --git a/tests/api/fleet/test_get_deckies.py b/tests/api/fleet/test_get_deckies.py
index 038b9965..9186986c 100644
--- a/tests/api/fleet/test_get_deckies.py
+++ b/tests/api/fleet/test_get_deckies.py
@@ -5,7 +5,7 @@ from hypothesis import given, settings, strategies as st
 from ..conftest import _FUZZ_SETTINGS
 
 @pytest.mark.anyio
-async def test_get_deckies_endpoint(mock_state_file, client: httpx.AsyncClient, auth_token: str):
+async def test_get_deckies_endpoint(mock_fleet_deckies, client: httpx.AsyncClient, auth_token: str):
     _response = await client.get("/api/v1/deckies", headers={"Authorization": f"Bearer {auth_token}"})
     assert _response.status_code == 200
     _data = _response.json()