feat(controller): expose instance-level fleet identity and health snapshots

Add a pure fleet snapshot assessor and a read-only controller/reconciler
MCP tool so multi-instance fleets can be enumerated by client_instance_id
without treating shared client_type as duplication. Trusted launcher
instance IDs, classification (missing/unmanifested/collisions/historical),
registry schema extensions, docs, and regression tests for #978.

Closes #978

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

docs/instance-fleet-identity.md

@@ -0,0 +1,171 @@
+# Instance-level fleet identity and health snapshots
+
+Issue **#978**. Companion primitives: **#948** (worker ownership), **#975**
+(heartbeat lifecycle), **#951** (restart receipts).
+
+## Why this exists
+
+The multi-instance fleet gate (#963) needs a *native* answer to:
+
+* which application launches are live;
+* which of the five namespace workers belong to each launch;
+* whether two Codex (or Claude, Grok, …) launches are distinct;
+* whether any live collision is real rather than a shared client type.
+
+Process tables, PID proximity, configuration files, and direct SQLite access
+are **not** production evidence. The sanctioned surface is the read-only MCP
+tool `gitea_snapshot_instance_fleet` on **controller** and **reconciler**
+namespaces.
+
+## Identity hierarchy
+
+| Identity | Scope | Who generates it | Lifetime |
+| --- | --- | --- | --- |
+| `client_type` | Application family (`codex`, `claude_code`, `gemini`, `grok`, …) | Launcher sets `GITEA_MCP_CLIENT` | Stable for the product |
+| `client_instance_id` | One running application launch | **Trusted launcher**, once per launch, as `GITEA_MCP_CLIENT_INSTANCE` | Fresh launch → new ID; reconnect of same launch → same ID; full app restart → new ID |
+| `fleet_run_id` | Operator-approved enrollment / canary cohort | Operator / controller sets `GITEA_MCP_FLEET_RUN_ID` | Duration of the approved rollout |
+| `namespace` | `author` \| `reviewer` \| `merger` \| `controller` \| `reconciler` | Profile / MCP server binding | Process lifetime |
+| `worker_id` / `worker_identity` | One namespace worker process | Runtime registry at first registration | New on worker restart; not reused |
+| `session_id` | Client session ownership | Launcher `GITEA_MCP_CLIENT_SESSION` or runtime | Session lifetime |
+| `generation_id` | One daemon launch | Runtime at process boot | New on process restart |
+| `process_identity` / PID | OS process | Runtime | Process lifetime |
+
+### Rules
+
+1. Multiple active instances **may** share the same `client_type`.
+2. Every application launch receives a **distinct** `client_instance_id`.
+3. All five namespace workers of one launch report the **same**
+   `client_instance_id`.
+4. Each namespace worker has a **distinct** `worker_identity`, process
+   identity, generation, and PID.
+5. Instance identity is **never** inferred from PID proximity, timestamps, or
+   client type alone.
+6. Live reuse of one `client_instance_id` with conflicting workers fails closed.
+7. Sharing only a profile or `client_type` is **not** a duplicate.
+
+This deliberately **replaces** any permanent `exactly_one_per_profile` fleet
+model (#949 assumption) as the operating rule for multi-instance fleets.
+
+## How five workers join one instance
+
+1. The host starts one application instance (for example one Codex session).
+2. The trusted launcher mints `client_instance_id` (see
+   `mcp_fleet_snapshot.generate_client_instance_id`) and injects:
+
+   ```text
+   GITEA_MCP_CLIENT=<client_type>
+   GITEA_MCP_CLIENT_INSTANCE=<client_instance_id>
+   GITEA_MCP_CLIENT_SESSION=<session_id>          # optional but recommended
+   GITEA_MCP_FLEET_RUN_ID=<enrollment id>         # when on an approved canary
+   ```
+
+3. The launcher starts the five MCP namespace processes (or attaches five
+   role profiles) with **that same environment**.
+4. Each worker registers once into the worker registry with its own
+   `worker_identity`, `namespace`, `generation_id`, and PID, but the shared
+   `client_instance_id`.
+
+Worker reconnect (same process, same registration) keeps the instance ID.
+Worker restart (new process) mints a new worker identity and generation but
+must still receive the same `GITEA_MCP_CLIENT_INSTANCE` from the parent
+application if it is the same launch. Full application restart mints a new
+`client_instance_id`.
+
+## Approved fleet manifest
+
+An operator (or controller enrollment step) obtains an approved manifest as a
+list of expected instances, for example:
+
+```json
+{
+  "instances": [
+    {
+      "client_type": "codex",
+      "client_instance_id": "inst-codex-20260730T120000Z-abc123def456",
+      "fleet_run_id": "canary-963-2026-07-30",
+      "namespaces": ["author", "reviewer", "merger", "controller", "reconciler"]
+    },
+    {
+      "client_type": "codex",
+      "client_instance_id": "inst-codex-20260730T120100Z-fed654cba321",
+      "fleet_run_id": "canary-963-2026-07-30",
+      "namespaces": ["author", "reviewer", "merger", "controller", "reconciler"]
+    }
+  ]
+}
+```
+
+Pass that list as `expected_manifest` to `gitea_snapshot_instance_fleet`.
+When a manifest is supplied:
+
+* instances on the manifest but not live → `missing_expected`;
+* live instances not on the manifest → `unmanifested`;
+* both are **active blockers** for fleet-gate safety.
+
+Without a manifest, the snapshot still enumerates the live fleet and classifies
+identity collisions; it does not invent enrollment policy.
+
+## Snapshot consistency
+
+Each snapshot includes:
+
+* `snapshot_at` — UTC timestamp;
+* `consistency_token` / `registry_revision` — content digest over worker
+  identity, instance id, status, heartbeat, fencing, and generation.
+
+Two successive snapshots can prove heartbeat continuity via
+`mcp_fleet_snapshot.compare_snapshot_heartbeats`.
+
+## Classification (active vs historical)
+
+**Active blockers** (make `live_fleet_safe=false`):
+
+* missing expected instance;
+* unmanifested extra instance;
+* duplicate namespace worker within one instance;
+* live `client_instance_id` collision;
+* reused worker / session / generation / process / PID / fencing identity;
+* orphaned or unowned workers;
+* unknown client;
+* foreign-repository workers;
+* old-revision workers;
+* stale workers still marked active;
+* legacy incomplete instance identity.
+
+**Historical dead rows** (`status` released/superseded) are reported as
+`historical_dead` findings with `active_blocker=false`. They never
+automatically make the live fleet unsafe.
+
+## Fail-closed behaviour and recovery
+
+| Condition | Mutation safety | Diagnostic reads | Recovery |
+| --- | --- | --- | --- |
+| Two instances, same `client_type`, distinct IDs | Safe (if otherwise healthy) | Available | None needed |
+| Live reuse of one `client_instance_id` | Unsafe | Available | Stop the colliding launch or re-issue a distinct ID |
+| Two workers, same namespace, one instance | Unsafe | Available | Stop the extra worker |
+| Legacy registration without trusted instance ID | Unsafe for fleet mutation | Available | Relaunch with launcher-issued `GITEA_MCP_CLIENT_INSTANCE` |
+| Historical dead row only | Does not block alone | Available | No action required for fleet safety |
+| Registry unavailable | Snapshot fails closed | N/A | Repair registry path / reconnect namespaces |
+
+Incomplete or untrusted instance identity **cannot** authorize unsafe
+mutation. Diagnostic reads remain available where `gitea.read` allows.
+
+## Permissions
+
+* **Allowed:** `controller`, `reconciler` with `gitea.read`.
+* **Denied:** author, reviewer, merger (even with `gitea.read` for other tools).
+* **No new mutation permissions** are granted to any role.
+
+## Related surfaces
+
+* `mcp_worker_identity` — registry, worker identity, heartbeats (#948, #975).
+* `mcp_fleet_snapshot` — pure snapshot + classification (#978).
+* `gitea_snapshot_instance_fleet` — sanctioned MCP tool (#978).
+* `gitea_get_runtime_context` — single-process view (not fleet-wide).
+
+## Non-goals
+
+* Starting the #963 canary.
+* Purging historical registry rows.
+* Preserving “exactly one process per profile” as the permanent model.
+* Using shell / process-table / SQLite inspection as production fleet evidence.

docs/mcp-tool-inventory.md

@@ -159,6 +159,7 @@ that gates each call, not which tools exist.
 - `gitea_sentry_reconcile_issue`
 - `gitea_sentry_watchdog`
 - `gitea_set_issue_labels`
+- `gitea_snapshot_instance_fleet`
 - `gitea_submit_pr_review`
 - `gitea_update_pr_branch_by_merge`
 - `gitea_validate_review_final_report`

gitea_config.py

@@ -1203,6 +1203,9 @@ RECOGNIZED_GITEA_ENV_KEYS = frozenset({
     "GITEA_MCP_CLIENT",
     "GITEA_MCP_CLIENT_INSTANCE",
     "GITEA_MCP_CLIENT_SESSION",
+    # #978: operator-approved fleet enrollment identity shared by one launch.
+    "GITEA_MCP_FLEET_RUN_ID",
+    "GITEA_MCP_PROCESS_IDENTITY",
     # #975 review 652 B1: production also consumes HEARTBEAT_INTERVAL_ENV from
     # mcp_worker_identity via gitea_mcp_server._start_worker_heartbeat. Omitting
     # it reproduced the same unsupported-env → runtime_reconnect_required

gitea_mcp_server.py

@@ -15733,6 +15733,7 @@ _WORKER_HEARTBEAT_SUPERVISOR = None
 CLIENT_NAME_ENV = "GITEA_MCP_CLIENT"
 CLIENT_INSTANCE_ENV = "GITEA_MCP_CLIENT_INSTANCE"
 CLIENT_SESSION_ENV = "GITEA_MCP_CLIENT_SESSION"
+FLEET_RUN_ENV = "GITEA_MCP_FLEET_RUN_ID"
 
 
 def _worker_registry():
@@ -15756,13 +15757,34 @@ def _worker_registry():
 
 
 def _client_identity_hints() -> dict:
-    """What the launcher told us about itself. Unset fields stay unset."""
+    """What the launcher told us about itself (#948 / #975 / #978).
+
+    ``client_instance_id`` is established by the trusted application launcher
+    once per launch and shared by all five namespace workers. When the launcher
+    key is absent we still register under an explicit *legacy* placeholder so
+    diagnostic reads work, but the registration is marked incomplete and cannot
+    authorize multi-instance fleet mutation safety.
+    """
+    import mcp_fleet_snapshot
+
+    client_name = (os.environ.get(CLIENT_NAME_ENV) or "").strip() or None
+    raw_instance = (os.environ.get(CLIENT_INSTANCE_ENV) or "").strip() or None
+    instance = mcp_fleet_snapshot.assess_instance_identity(raw_instance)
+    # Legacy placeholder only when the launcher omitted the key — never invent a
+    # trusted ID from PID proximity.
+    if not instance["client_instance_id"]:
+        placeholder = f"legacy-pid-{os.getpid()}"
+        instance = mcp_fleet_snapshot.assess_instance_identity(
+            placeholder, source="pid_fallback"
+        )
     return {
-        "client_name": (os.environ.get(CLIENT_NAME_ENV) or "").strip() or None,
-        "client_instance_id": (os.environ.get(CLIENT_INSTANCE_ENV) or "").strip()
-        or f"pid-{os.getpid()}",
+        "client_name": client_name,
+        "client_instance_id": instance["client_instance_id"],
+        "instance_id_provenance": instance["provenance"],
+        "instance_identity_trusted": instance["trusted"],
         "session_id": (os.environ.get(CLIENT_SESSION_ENV) or "").strip()
         or f"proc-{os.getpid()}-{_process_boot_head_sha or 'nohead'}",
+        "fleet_run_id": (os.environ.get(FLEET_RUN_ENV) or "").strip() or None,
     }
 
 
@@ -15794,20 +15816,43 @@ def _active_worker_identity() -> str | None:
             identity = mcp_worker_identity.generate_worker_identity(
                 hints["client_name"], hints["session_id"]
             )
+            role = _active_role_kind_safe()
+            profile_name = (
+                (os.environ.get(gitea_config.ENV_PROFILE) or "").strip() or None
+            )
+            # Namespace is the role namespace (author/reviewer/…) when known.
+            namespace = role if role in {
+                "author", "reviewer", "merger", "controller", "reconciler"
+            } else None
+            parity = None
+            try:
+                parity = _current_master_parity()
+            except Exception:
+                parity = None
             outcome = registry.register(
                 worker_identity=identity,
                 client_name=hints["client_name"],
                 client_instance_id=hints["client_instance_id"],
                 session_id=hints["session_id"],
                 generation_id=generation,
-                role=_active_role_kind_safe(),
-                profile=(os.environ.get(gitea_config.ENV_PROFILE) or "").strip() or None,
+                role=role,
+                profile=profile_name,
+                namespace=namespace,
                 remote=(os.environ.get("GITEA_MCP_REMOTE") or "").strip() or None,
                 repository_binding=PROJECT_ROOT,
                 pid=os.getpid(),
                 transport=native.get("bound_transport"),
                 token_fingerprint=native.get("token_fingerprint"),
                 pid_alive_probe=issue_lock_store.is_process_alive,
+                fleet_run_id=hints.get("fleet_run_id"),
+                process_identity=f"pid-{os.getpid()}",
+                startup_revision=(parity or {}).get("startup_head")
+                or _process_boot_head_sha,
+                loaded_revision=(parity or {}).get("local_head")
+                or (parity or {}).get("current_head"),
+                parity_revision=(parity or {}).get("current_head"),
+                live_revision=(parity or {}).get("live_remote_head"),
+                instance_id_provenance=hints.get("instance_id_provenance"),
             )
             if outcome.get("registered"):
                 _WORKER_IDENTITY = identity
@@ -19373,6 +19418,172 @@ def gitea_validate_review_final_report(
     )
 
 
+@mcp.tool()
+def gitea_snapshot_instance_fleet(
+    remote: str = "dadeschools",
+    host: str | None = None,
+    org: str | None = None,
+    repo: str | None = None,
+    expected_manifest: list | dict | str | None = None,
+    include_historical: bool = True,
+    canonical_repository: str | None = None,
+    expected_live_revision: str | None = None,
+) -> dict:
+    """Read-only: authoritative instance-level fleet identity and health snapshot (#978).
+
+    Controller and reconciler only. Returns a point-in-time snapshot of every
+    registered namespace worker with instance attribution, heartbeat freshness,
+    and structured classification (expected/missing/unmanifested, duplicate
+    namespace workers, identity collisions, foreign repository, old revision,
+    historical dead rows). Sharing only a client type is never a duplicate.
+
+    Does not grant any mutation capability. Does not scan process tables or
+    open foreign databases for production evidence — the worker registry is
+    the sole authority.
+
+    Args:
+        remote: Known instance — 'dadeschools' or 'prgs'.
+        host: Optional host override.
+        org: Optional org override (audit context only).
+        repo: Optional repo override (audit context only).
+        expected_manifest: Optional approved fleet enrollment list
+            (list of dicts with client_instance_id / client_type / fleet_run_id).
+            When supplied, missing and unmanifested instances are classified.
+        include_historical: Include released/superseded rows (default True);
+            historical rows never make the live fleet unsafe by themselves.
+        canonical_repository: Expected repository binding path/slug for
+            foreign-repository classification.
+        expected_live_revision: When set, workers whose recorded revisions
+            differ are classified as old-revision.
+    """
+    import json as _json
+
+    import mcp_fleet_snapshot
+
+    read_block = _profile_operation_gate("gitea.read")
+    if read_block:
+        return {
+            "success": False,
+            "read_only": True,
+            "reasons": read_block,
+            "permission_report": _permission_block_report("gitea.read"),
+        }
+
+    profile = get_profile()
+    role = _profile_role_kind(profile)
+    if role not in {"controller", "reconciler"}:
+        return {
+            "success": False,
+            "read_only": True,
+            "allowed": False,
+            "denied_role": role,
+            "required_roles": ["controller", "reconciler"],
+            "mutation_performed": False,
+            "reasons": [
+                f"gitea_snapshot_instance_fleet is restricted to controller and "
+                f"reconciler roles; active role_kind is {role!r}. Author, "
+                "reviewer, and merger profiles keep gitea.read for diagnosis "
+                "elsewhere but do not receive this fleet surface, and no "
+                "unrelated mutation permission is granted."
+            ],
+            "exact_next_action": (
+                "Re-run from a prgs-controller or prgs-reconciler namespace."
+            ),
+        }
+
+    manifest: list | None = None
+    if expected_manifest is not None:
+        raw = expected_manifest
+        if isinstance(raw, str):
+            try:
+                raw = _json.loads(raw)
+            except Exception as exc:
+                return {
+                    "success": False,
+                    "read_only": True,
+                    "reasons": [
+                        f"expected_manifest is not valid JSON: {type(exc).__name__}"
+                    ],
+                }
+        if isinstance(raw, dict):
+            # Accept {"instances": [...]} or a single instance object.
+            if "instances" in raw and isinstance(raw["instances"], list):
+                raw = raw["instances"]
+            else:
+                raw = [raw]
+        if not isinstance(raw, list):
+            return {
+                "success": False,
+                "read_only": True,
+                "reasons": ["expected_manifest must be a list of instance objects"],
+            }
+        manifest = raw
+
+    registry = _worker_registry()
+    if registry is None:
+        return {
+            "success": False,
+            "read_only": True,
+            "reasons": [
+                "worker registry is unavailable; cannot produce an authoritative "
+                "fleet snapshot (fail closed)"
+            ],
+            "exact_next_action": (
+                "Ensure GITEA_WORKER_REGISTRY_DB is writable and re-run after "
+                "workers have registered."
+            ),
+        }
+
+    try:
+        if include_historical:
+            records = registry.list_workers(status=None)
+        else:
+            records = registry.list_workers(status=mcp_worker_identity.STATUS_ACTIVE)
+    except Exception as exc:
+        return {
+            "success": False,
+            "read_only": True,
+            "reasons": [
+                f"failed to read worker registry: {type(exc).__name__}: {_redact(str(exc))}"
+            ],
+        }
+
+    parity = None
+    try:
+        parity = _current_master_parity()
+    except Exception:
+        parity = None
+    live_rev = expected_live_revision or (parity or {}).get("live_remote_head")
+    canon = canonical_repository or PROJECT_ROOT
+
+    snapshot = mcp_fleet_snapshot.snapshot_instance_fleet(
+        records,
+        expected_manifest=manifest,
+        pid_alive_probe=issue_lock_store.is_process_alive,
+        canonical_repository=canon,
+        expected_live_revision=live_rev,
+    )
+    snapshot["role_kind"] = role
+    snapshot["profile"] = profile.get("profile_name")
+    snapshot["remote"] = _effective_remote(remote)
+    snapshot["repository"] = {
+        "org": org,
+        "repo": repo,
+        "canonical_repository": canon,
+    }
+    snapshot["mutation_performed"] = False
+    snapshot["permission_scope"] = {
+        "read_only": True,
+        "granted_operations": ["gitea.read"],
+        "denied_unrelated_mutations": True,
+        "note": (
+            "This capability is strictly observational. It does not authorize "
+            "branch, issue, PR, review, merge, or restart mutations."
+        ),
+    }
+    return snapshot
+
+
 @mcp.tool()
 def gitea_get_runtime_context(
     remote: str = "dadeschools",

mcp_fleet_snapshot.py

@@ -0,0 +1,847 @@
+"""Instance-level fleet identity and health snapshots (#978).
+
+#948 established per-worker ownership; #975 made heartbeats keep those rows
+live. Neither surface could enumerate the fleet at *instance* granularity:
+which application launch owns which five namespace workers, whether two
+Codex launches are distinct, or whether a live collision is real rather than
+a shared client type.
+
+This module is pure. Callers supply registry rows (and optional enrichments);
+nothing here opens SQLite, scans process tables, or mutates state. Production
+evidence for the fleet gate is the snapshot returned by the sanctioned
+controller/reconciler tool that wraps this assessor.
+
+Identity hierarchy (highest → lowest):
+
+* ``client_type`` — application family (``codex``, ``claude_code``, …)
+* ``client_instance_id`` — one running application launch (trusted launcher)
+* ``fleet_run_id`` — operator-approved enrollment / canary cohort
+* ``worker_id`` / ``worker_identity`` — one namespace worker process
+* ``namespace`` — author | reviewer | merger | controller | reconciler
+
+Multiple simultaneous instances of the same ``client_type`` are first-class.
+Sharing only a profile or client type is never a duplicate.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import secrets
+from collections import defaultdict
+from datetime import datetime, timezone
+from typing import Any, Callable, Iterable, Mapping
+
+import mcp_worker_identity as mwi
+
+# --- Classification labels ------------------------------------------------
+
+CLASS_EXPECTED = "expected_enrolled"
+CLASS_MISSING = "missing_expected"
+CLASS_UNMANIFESTED = "unmanifested"
+CLASS_DUPLICATE_NAMESPACE = "duplicate_namespace_worker"
+CLASS_INSTANCE_ID_COLLISION = "instance_id_collision"
+CLASS_WORKER_ID_COLLISION = "worker_identity_collision"
+CLASS_SESSION_COLLISION = "session_identity_collision"
+CLASS_GENERATION_COLLISION = "generation_identity_collision"
+CLASS_PROCESS_COLLISION = "process_identity_collision"
+CLASS_PID_COLLISION = "pid_collision"
+CLASS_OWNERSHIP_COLLISION = "ownership_fencing_collision"
+CLASS_ORPHANED = "orphaned_unowned"
+CLASS_UNKNOWN_CLIENT = "unknown_client"
+CLASS_FOREIGN_REPOSITORY = "foreign_repository"
+CLASS_OLD_REVISION = "old_revision"
+CLASS_STALE_WORKER = "stale_orphaned_worker"
+CLASS_LEGACY_INCOMPLETE = "legacy_incomplete_identity"
+CLASS_HISTORICAL = "historical_dead"
+CLASS_HEALTHY = "healthy"
+
+#: Active blockers that make the live fleet unsafe for mutation-gated work.
+ACTIVE_BLOCKER_CLASSES = frozenset(
+    {
+        CLASS_MISSING,
+        CLASS_UNMANIFESTED,
+        CLASS_DUPLICATE_NAMESPACE,
+        CLASS_INSTANCE_ID_COLLISION,
+        CLASS_WORKER_ID_COLLISION,
+        CLASS_SESSION_COLLISION,
+        CLASS_GENERATION_COLLISION,
+        CLASS_PROCESS_COLLISION,
+        CLASS_PID_COLLISION,
+        CLASS_OWNERSHIP_COLLISION,
+        CLASS_ORPHANED,
+        CLASS_UNKNOWN_CLIENT,
+        CLASS_FOREIGN_REPOSITORY,
+        CLASS_OLD_REVISION,
+        CLASS_STALE_WORKER,
+        CLASS_LEGACY_INCOMPLETE,
+    }
+)
+
+SANCTIONED_NAMESPACES = frozenset(
+    {"author", "reviewer", "merger", "controller", "reconciler"}
+)
+
+INSTANCE_ID_PROVENANCE_TRUSTED = "trusted_launcher"
+INSTANCE_ID_PROVENANCE_LEGACY = "legacy_incomplete"
+INSTANCE_ID_PROVENANCE_MISSING = "missing"
+
+CLIENT_INSTANCE_ENV = "GITEA_MCP_CLIENT_INSTANCE"
+FLEET_RUN_ENV = "GITEA_MCP_FLEET_RUN_ID"
+PROCESS_IDENTITY_ENV = "GITEA_MCP_PROCESS_IDENTITY"
+
+_LEGACY_INSTANCE_PREFIXES = ("pid-", "proc-", "legacy-")
+
+
+def _utc_now() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+def _ts(value: datetime) -> str:
+    return value.astimezone(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
+
+
+def generate_client_instance_id(
+    client_type: str | None,
+    *,
+    launch_nonce: str | None = None,
+    now: datetime | None = None,
+) -> str:
+    """Mint a distinct instance ID for one application launch (#978).
+
+    The trusted launcher (or host that starts all five namespace workers)
+    generates this once per launch and injects it as ``GITEA_MCP_CLIENT_INSTANCE``
+    into every worker environment. Workers never invent their own instance ID
+    from PID proximity or timestamps.
+    """
+    client = mwi.normalize_client_name(client_type)
+    stamp = (now or _utc_now()).astimezone(timezone.utc).strftime(
+        mwi.IDENTITY_TIMESTAMP_FORMAT
+    )
+    nonce = launch_nonce if launch_nonce is not None else secrets.token_hex(16)
+    digest = hashlib.sha256(
+        f"{client}\x1f{stamp}\x1f{nonce}".encode("utf-8")
+    ).hexdigest()[:12]
+    return f"inst-{client}-{stamp}-{digest}"
+
+
+def assess_instance_identity(
+    raw_instance_id: str | None,
+    *,
+    source: str | None = None,
+) -> dict[str, Any]:
+    """Classify whether a client_instance_id is trusted enough for mutation.
+
+    Trusted instance IDs are non-empty and not the pre-#978 PID/proc fallbacks.
+    Incomplete identities remain visible for diagnosis but cannot authorize
+    unsafe mutation.
+    """
+    text = (raw_instance_id or "").strip()
+    if not text:
+        return {
+            "client_instance_id": None,
+            "complete": False,
+            "trusted": False,
+            "provenance": INSTANCE_ID_PROVENANCE_MISSING,
+            "reasons": [
+                "client_instance_id is missing; the trusted launcher must set "
+                f"{CLIENT_INSTANCE_ENV} once per application launch"
+            ],
+        }
+    lowered = text.lower()
+    if lowered.startswith(_LEGACY_INSTANCE_PREFIXES) or source == "pid_fallback":
+        return {
+            "client_instance_id": text,
+            "complete": False,
+            "trusted": False,
+            "provenance": INSTANCE_ID_PROVENANCE_LEGACY,
+            "reasons": [
+                f"client_instance_id {text!r} is a legacy PID/process fallback, "
+                "not a trusted launcher-issued instance identity"
+            ],
+        }
+    return {
+        "client_instance_id": text,
+        "complete": True,
+        "trusted": True,
+        "provenance": INSTANCE_ID_PROVENANCE_TRUSTED,
+        "reasons": [],
+    }
+
+
+def resolve_client_instance_from_env(
+    env: Mapping[str, str] | None = None,
+    *,
+    pid: int | None = None,
+) -> dict[str, Any]:
+    """Resolve instance identity from launcher env without inventing one.
+
+    When the trusted key is absent, return incomplete evidence rather than a
+    silent ``pid-<n>`` identity. Callers that still need a non-empty registry
+    key may choose a legacy placeholder deliberately; they must not treat it as
+    trusted.
+    """
+    source = dict(env or {})
+    raw = (source.get(CLIENT_INSTANCE_ENV) or "").strip()
+    assessment = assess_instance_identity(raw or None)
+    assessment["fleet_run_id"] = (source.get(FLEET_RUN_ENV) or "").strip() or None
+    assessment["process_identity"] = (
+        (source.get(PROCESS_IDENTITY_ENV) or "").strip()
+        or (f"pid-{pid}" if pid is not None else None)
+    )
+    return assessment
+
+
+def _public_worker(record: Mapping[str, Any]) -> dict[str, Any]:
+    return {
+        "worker_id": record.get("worker_identity") or record.get("worker_id"),
+        "worker_identity": record.get("worker_identity") or record.get("worker_id"),
+        "client_type": mwi.normalize_client_name(
+            record.get("client_name") or record.get("client_type")
+        ),
+        "client_instance_id": record.get("client_instance_id"),
+        "fleet_run_id": record.get("fleet_run_id"),
+        "namespace": record.get("namespace"),
+        "profile": record.get("profile"),
+        "declared_role": record.get("role") or record.get("declared_role"),
+        "authenticated_account": record.get("authenticated_account"),
+        "session_id": record.get("session_id"),
+        "generation_id": record.get("generation_id"),
+        "process_identity": record.get("process_identity")
+        or (
+            f"pid-{record['pid']}"
+            if record.get("pid") is not None
+            else None
+        ),
+        "pid": record.get("pid"),
+        "repository_binding": record.get("repository_binding"),
+        "remote": record.get("remote"),
+        "startup_revision": record.get("startup_revision"),
+        "loaded_revision": record.get("loaded_revision"),
+        "parity_revision": record.get("parity_revision"),
+        "live_revision": record.get("live_revision"),
+        "runtime_provenance": record.get("runtime_provenance")
+        or record.get("transport"),
+        "transport": record.get("transport"),
+        "started_at": record.get("started_at"),
+        "last_heartbeat_at": record.get("last_heartbeat_at"),
+        "heartbeat_ttl_seconds": record.get("heartbeat_ttl_seconds"),
+        "fencing_epoch": record.get("fencing_epoch"),
+        "status": record.get("status"),
+        "instance_id_provenance": record.get("instance_id_provenance"),
+    }
+
+
+def _liveness(
+    record: Mapping[str, Any],
+    *,
+    now: datetime | None,
+    pid_alive_probe: Callable[[int | None], bool | None] | None,
+) -> dict[str, Any]:
+    pid_alive = None
+    if pid_alive_probe is not None and record.get("pid") is not None:
+        try:
+            pid_alive = pid_alive_probe(record.get("pid"))
+        except Exception:
+            pid_alive = None
+    return mwi.WorkerRegistry.is_live(record, now=now, pid_alive=pid_alive)
+
+
+def _consistency_token(rows: Iterable[Mapping[str, Any]], snapshot_at: str) -> str:
+    material = [snapshot_at]
+    for row in sorted(
+        rows,
+        key=lambda r: (
+            str(r.get("worker_identity") or ""),
+            str(r.get("last_heartbeat_at") or ""),
+            str(r.get("fencing_epoch") or ""),
+        ),
+    ):
+        material.append(
+            "|".join(
+                [
+                    str(row.get("worker_identity") or ""),
+                    str(row.get("client_instance_id") or ""),
+                    str(row.get("status") or ""),
+                    str(row.get("last_heartbeat_at") or ""),
+                    str(row.get("fencing_epoch") or ""),
+                    str(row.get("generation_id") or ""),
+                ]
+            )
+        )
+    digest = hashlib.sha256("\n".join(material).encode("utf-8")).hexdigest()[:16]
+    return f"fleetrev-{digest}"
+
+
+def build_worker_snapshot_row(
+    record: Mapping[str, Any],
+    *,
+    now: datetime | None = None,
+    pid_alive_probe: Callable[[int | None], bool | None] | None = None,
+    canonical_repository: str | None = None,
+    expected_live_revision: str | None = None,
+    heartbeat_supervised: bool | None = None,
+) -> dict[str, Any]:
+    """One point-in-time worker row for the fleet snapshot."""
+    stamp = now or _utc_now()
+    base = _public_worker(record)
+    identity = assess_instance_identity(
+        base.get("client_instance_id"),
+        source=record.get("instance_id_source"),
+    )
+    liveness = _liveness(record, now=stamp, pid_alive_probe=pid_alive_probe)
+    is_historical = str(record.get("status") or "") != mwi.STATUS_ACTIVE
+    live = bool(liveness.get("live")) and not is_historical
+
+    repo = (base.get("repository_binding") or "").strip() or None
+    foreign_repo = bool(
+        canonical_repository
+        and repo
+        and repo.rstrip("/") != str(canonical_repository).rstrip("/")
+    )
+    old_revision = False
+    if expected_live_revision:
+        for key in ("startup_revision", "loaded_revision", "parity_revision", "live_revision"):
+            rev = (base.get(key) or "").strip()
+            if rev and rev != expected_live_revision:
+                old_revision = True
+                break
+
+    ownership_state = "historical" if is_historical else (
+        "live" if live else "stale"
+    )
+    if live and not identity["trusted"]:
+        ownership_state = "live_untrusted_identity"
+    if live and not base.get("session_id"):
+        ownership_state = "orphaned"
+
+    mutation_safe = bool(
+        live
+        and identity["trusted"]
+        and not foreign_repo
+        and not old_revision
+        and ownership_state == "live"
+        and base.get("client_type") != mwi.UNKNOWN_CLIENT
+    )
+
+    restart_required = bool(
+        old_revision
+        or (live and not liveness.get("heartbeat_fresh", True))
+    )
+
+    return {
+        **base,
+        "instance_identity": identity,
+        "client_instance_id": identity["client_instance_id"] or base.get("client_instance_id"),
+        "instance_id_provenance": identity["provenance"],
+        "instance_identity_trusted": identity["trusted"],
+        "live": live,
+        "historical": is_historical,
+        "liveness": liveness,
+        "heartbeat": {
+            "registered": bool(base.get("last_heartbeat_at")),
+            "supervised": heartbeat_supervised,
+            "age_seconds": liveness.get("heartbeat_age_seconds"),
+            "ttl_seconds": liveness.get("heartbeat_ttl_seconds"),
+            "fresh": liveness.get("heartbeat_fresh"),
+            "last_heartbeat_at": base.get("last_heartbeat_at"),
+        },
+        "fencing": {
+            "fencing_epoch": base.get("fencing_epoch"),
+            "generation_id": base.get("generation_id"),
+        },
+        "ownership_state": ownership_state,
+        "foreign_repository": foreign_repo,
+        "old_revision": old_revision,
+        "stale": not live and not is_historical,
+        "restart_required": restart_required,
+        "mutation_safe": mutation_safe,
+        "conflicting_live_sessions": [],
+    }
+
+
+def _collision_groups(
+    live_rows: list[dict[str, Any]],
+    key_fn,
+) -> dict[str, list[dict[str, Any]]]:
+    groups: dict[str, list[dict[str, Any]]] = defaultdict(list)
+    for row in live_rows:
+        key = key_fn(row)
+        if key is None or key == "" or key == "None":
+            continue
+        groups[str(key)].append(row)
+    return {k: v for k, v in groups.items() if len(v) > 1}
+
+
+def snapshot_instance_fleet(
+    records: Iterable[Mapping[str, Any]],
+    *,
+    expected_manifest: list[Mapping[str, Any]] | None = None,
+    now: datetime | None = None,
+    pid_alive_probe: Callable[[int | None], bool | None] | None = None,
+    canonical_repository: str | None = None,
+    expected_live_revision: str | None = None,
+    registry_revision: str | None = None,
+    known_client_types: Iterable[str] | None = None,
+) -> dict[str, Any]:
+    """Authoritative point-in-time fleet snapshot with classification (#978).
+
+    Historical dead rows are reported separately and never automatically make
+    the live fleet unsafe.
+    """
+    stamp = now or _utc_now()
+    snapshot_at = _ts(stamp)
+    known = {
+        mwi.normalize_client_name(c)
+        for c in (known_client_types or mwi.CLIENT_ALIASES.values())
+    }
+    known.discard(mwi.UNKNOWN_CLIENT)
+
+    all_rows: list[dict[str, Any]] = []
+    for record in records:
+        all_rows.append(
+            build_worker_snapshot_row(
+                record,
+                now=stamp,
+                pid_alive_probe=pid_alive_probe,
+                canonical_repository=canonical_repository,
+                expected_live_revision=expected_live_revision,
+            )
+        )
+
+    live_rows = [r for r in all_rows if r["live"]]
+    historical_rows = [r for r in all_rows if r["historical"]]
+    stale_rows = [r for r in all_rows if r["stale"]]
+
+    # --- identity collisions among live workers ---
+    findings: list[dict[str, Any]] = []
+
+    def _finding(
+        classification: str,
+        *,
+        severity: str,
+        workers: list[dict[str, Any]] | None = None,
+        instance_ids: list[str] | None = None,
+        detail: str,
+        active_blocker: bool,
+    ) -> None:
+        findings.append(
+            {
+                "classification": classification,
+                "severity": severity,
+                "active_blocker": active_blocker,
+                "detail": detail,
+                "client_instance_ids": instance_ids or sorted(
+                    {
+                        str(w.get("client_instance_id"))
+                        for w in (workers or [])
+                        if w.get("client_instance_id")
+                    }
+                ),
+                "worker_identities": [
+                    w.get("worker_identity") for w in (workers or [])
+                ],
+            }
+        )
+
+    # Duplicate worker identity (should not happen with PK, still detect)
+    for wid, group in _collision_groups(
+        live_rows, lambda r: r.get("worker_identity")
+    ).items():
+        _finding(
+            CLASS_WORKER_ID_COLLISION,
+            severity="blocker",
+            workers=group,
+            detail=f"worker identity {wid!r} is claimed by {len(group)} live workers",
+            active_blocker=True,
+        )
+
+    # Reused session identity across live workers
+    for sid, group in _collision_groups(live_rows, lambda r: r.get("session_id")).items():
+        # Same session may appear once; collision only when multiple workers share it
+        # across different worker identities (always true for group size > 1).
+        _finding(
+            CLASS_SESSION_COLLISION,
+            severity="blocker",
+            workers=group,
+            detail=f"session identity {sid!r} is reused by {len(group)} live workers",
+            active_blocker=True,
+        )
+
+    # Generation claimed by multiple live sessions/workers is a conflict when
+    # the workers are not the five sanctioned namespaces of one instance.
+    for gen, group in _collision_groups(
+        live_rows, lambda r: r.get("generation_id")
+    ).items():
+        namespaces = {g.get("namespace") for g in group if g.get("namespace")}
+        instance_ids = {g.get("client_instance_id") for g in group}
+        # Multiple workers under one generation is only valid if they share one
+        # instance and distinct namespaces. Same generation + same namespace = bad.
+        by_ns: dict[str, list] = defaultdict(list)
+        for g in group:
+            by_ns[str(g.get("namespace") or "")].append(g)
+        ns_dups = {ns: rows for ns, rows in by_ns.items() if ns and len(rows) > 1}
+        if ns_dups or len(instance_ids) > 1:
+            _finding(
+                CLASS_GENERATION_COLLISION,
+                severity="blocker",
+                workers=group,
+                detail=(
+                    f"generation {gen!r} is contested across namespaces/instances "
+                    f"(namespaces={sorted(namespaces)}, "
+                    f"instances={sorted(str(i) for i in instance_ids if i)})"
+                ),
+                active_blocker=True,
+            )
+
+    # Process identity / PID collisions across distinct workers
+    for proc, group in _collision_groups(
+        live_rows, lambda r: r.get("process_identity")
+    ).items():
+        if len({r.get("worker_identity") for r in group}) > 1:
+            _finding(
+                CLASS_PROCESS_COLLISION,
+                severity="blocker",
+                workers=group,
+                detail=f"process identity {proc!r} is shared by distinct live workers",
+                active_blocker=True,
+            )
+
+    for pid, group in _collision_groups(live_rows, lambda r: r.get("pid")).items():
+        if len({r.get("worker_identity") for r in group}) > 1:
+            _finding(
+                CLASS_PID_COLLISION,
+                severity="blocker",
+                workers=group,
+                detail=f"PID {pid} is shared by distinct live workers",
+                active_blocker=True,
+            )
+
+    # Fencing/ownership: same fencing epoch on different workers of different instances
+    for epoch, group in _collision_groups(
+        live_rows,
+        lambda r: (
+            f"{r.get('generation_id')}:{r.get('fencing_epoch')}"
+            if r.get("generation_id") is not None and r.get("fencing_epoch") is not None
+            else None
+        ),
+    ).items():
+        if len({r.get("client_instance_id") for r in group}) > 1:
+            _finding(
+                CLASS_OWNERSHIP_COLLISION,
+                severity="blocker",
+                workers=group,
+                detail=(
+                    f"fencing token {epoch!r} spans more than one client_instance_id"
+                ),
+                active_blocker=True,
+            )
+
+    # Per-instance grouping
+    by_instance: dict[str, list[dict[str, Any]]] = defaultdict(list)
+    unkeyed_live: list[dict[str, Any]] = []
+    for row in live_rows:
+        iid = row.get("client_instance_id")
+        if not iid:
+            unkeyed_live.append(row)
+            continue
+        by_instance[str(iid)].append(row)
+
+    instances: list[dict[str, Any]] = []
+    for iid, workers in sorted(by_instance.items()):
+        client_types = sorted({w.get("client_type") for w in workers if w.get("client_type")})
+        trusted = all(w.get("instance_identity_trusted") for w in workers)
+        namespaces = [w.get("namespace") for w in workers]
+        ns_counts: dict[str, int] = defaultdict(int)
+        for ns in namespaces:
+            if ns:
+                ns_counts[str(ns)] += 1
+        dup_ns = sorted(ns for ns, n in ns_counts.items() if n > 1)
+        if dup_ns:
+            _finding(
+                CLASS_DUPLICATE_NAMESPACE,
+                severity="blocker",
+                workers=[w for w in workers if w.get("namespace") in dup_ns],
+                instance_ids=[iid],
+                detail=(
+                    f"instance {iid!r} has more than one live worker for "
+                    f"namespace(s) {dup_ns}"
+                ),
+                active_blocker=True,
+            )
+
+        # Live reuse of one instance ID with incompatible client types
+        if len(client_types) > 1:
+            _finding(
+                CLASS_INSTANCE_ID_COLLISION,
+                severity="blocker",
+                workers=workers,
+                instance_ids=[iid],
+                detail=(
+                    f"client_instance_id {iid!r} is live under multiple client "
+                    f"types {client_types}"
+                ),
+                active_blocker=True,
+            )
+
+        if not trusted:
+            _finding(
+                CLASS_LEGACY_INCOMPLETE,
+                severity="blocker",
+                workers=workers,
+                instance_ids=[iid],
+                detail=(
+                    f"instance {iid!r} lacks trusted launcher-issued instance "
+                    "identity; diagnostic reads remain available"
+                ),
+                active_blocker=True,
+            )
+
+        unknown = [w for w in workers if w.get("client_type") == mwi.UNKNOWN_CLIENT]
+        if unknown:
+            _finding(
+                CLASS_UNKNOWN_CLIENT,
+                severity="blocker",
+                workers=unknown,
+                instance_ids=[iid],
+                detail=f"instance {iid!r} has worker(s) with unknown client_type",
+                active_blocker=True,
+            )
+
+        foreign = [w for w in workers if w.get("foreign_repository")]
+        if foreign:
+            _finding(
+                CLASS_FOREIGN_REPOSITORY,
+                severity="blocker",
+                workers=foreign,
+                instance_ids=[iid],
+                detail=f"instance {iid!r} has foreign-repository workers",
+                active_blocker=True,
+            )
+
+        old = [w for w in workers if w.get("old_revision")]
+        if old:
+            _finding(
+                CLASS_OLD_REVISION,
+                severity="blocker",
+                workers=old,
+                instance_ids=[iid],
+                detail=f"instance {iid!r} has old-revision workers",
+                active_blocker=True,
+            )
+
+        orphans = [w for w in workers if w.get("ownership_state") == "orphaned"]
+        if orphans:
+            _finding(
+                CLASS_ORPHANED,
+                severity="blocker",
+                workers=orphans,
+                instance_ids=[iid],
+                detail=f"instance {iid!r} has orphaned/unowned workers",
+                active_blocker=True,
+            )
+
+        instances.append(
+            {
+                "client_instance_id": iid,
+                "client_types": client_types,
+                "client_type": client_types[0] if len(client_types) == 1 else None,
+                "fleet_run_ids": sorted(
+                    {w.get("fleet_run_id") for w in workers if w.get("fleet_run_id")}
+                ),
+                "worker_count": len(workers),
+                "namespaces": sorted({n for n in namespaces if n}),
+                "namespace_counts": dict(ns_counts),
+                "duplicate_namespaces": dup_ns,
+                "trusted_instance_identity": trusted,
+                "workers": workers,
+                "mutation_safe": all(w.get("mutation_safe") for w in workers)
+                and not dup_ns
+                and trusted,
+            }
+        )
+
+    for row in unkeyed_live:
+        _finding(
+            CLASS_LEGACY_INCOMPLETE,
+            severity="blocker",
+            workers=[row],
+            detail="live worker has no client_instance_id",
+            active_blocker=True,
+        )
+        if row.get("client_type") == mwi.UNKNOWN_CLIENT:
+            _finding(
+                CLASS_UNKNOWN_CLIENT,
+                severity="blocker",
+                workers=[row],
+                detail="live worker has unknown client_type and no instance id",
+                active_blocker=True,
+            )
+
+    for row in stale_rows:
+        _finding(
+            CLASS_STALE_WORKER,
+            severity="warning",
+            workers=[row],
+            detail=(
+                f"worker {row.get('worker_identity')!r} is active in the registry "
+                "but not live (stale heartbeat or dead pid)"
+            ),
+            active_blocker=True,
+        )
+
+    for row in historical_rows:
+        _finding(
+            CLASS_HISTORICAL,
+            severity="info",
+            workers=[row],
+            detail=(
+                f"historical registration {row.get('worker_identity')!r} "
+                f"(status={row.get('status')!r}) is not an active blocker"
+            ),
+            active_blocker=False,
+        )
+
+    # Manifest comparison
+    expected = list(expected_manifest or [])
+    expected_ids = {
+        str(item.get("client_instance_id")).strip()
+        for item in expected
+        if (item.get("client_instance_id") or "").strip()
+    }
+    live_ids = set(by_instance.keys())
+    missing_ids = sorted(expected_ids - live_ids)
+    unmanifested_ids = sorted(live_ids - expected_ids) if expected_ids else []
+
+    for iid in missing_ids:
+        _finding(
+            CLASS_MISSING,
+            severity="blocker",
+            instance_ids=[iid],
+            detail=f"expected enrolled instance {iid!r} is missing from the live fleet",
+            active_blocker=True,
+        )
+    for iid in unmanifested_ids:
+        _finding(
+            CLASS_UNMANIFESTED,
+            severity="blocker",
+            instance_ids=[iid],
+            workers=by_instance.get(iid, []),
+            detail=(
+                f"live instance {iid!r} is not on the approved fleet manifest "
+                "(unmanifested)"
+            ),
+            active_blocker=True,
+        )
+
+    # Same client_type multi-instance is healthy when each has distinct instance IDs
+    by_type: dict[str, list[str]] = defaultdict(list)
+    for inst in instances:
+        for ct in inst.get("client_types") or []:
+            by_type[str(ct)].append(inst["client_instance_id"])
+    multi_instance_same_type = {
+        ct: ids for ct, ids in by_type.items() if len(ids) > 1
+    }
+
+    active_blockers = [f for f in findings if f.get("active_blocker")]
+    historical_only = [f for f in findings if f.get("classification") == CLASS_HISTORICAL]
+    live_safe = not active_blockers
+
+    consistency = registry_revision or _consistency_token(all_rows, snapshot_at)
+
+    return {
+        "success": True,
+        "read_only": True,
+        "snapshot_at": snapshot_at,
+        "consistency_token": consistency,
+        "registry_revision": consistency,
+        "live_worker_count": len(live_rows),
+        "historical_worker_count": len(historical_rows),
+        "stale_worker_count": len(stale_rows),
+        "instance_count": len(instances),
+        "workers": all_rows,
+        "live_workers": live_rows,
+        "historical_workers": historical_rows,
+        "stale_workers": stale_rows,
+        "instances": instances,
+        "multi_instance_same_client_type": multi_instance_same_type,
+        "same_client_type_not_duplicate": True,
+        "expected_manifest": [
+            {
+                "client_instance_id": item.get("client_instance_id"),
+                "client_type": item.get("client_type"),
+                "fleet_run_id": item.get("fleet_run_id"),
+                "namespaces": item.get("namespaces"),
+            }
+            for item in expected
+        ],
+        "missing_expected_instance_ids": missing_ids,
+        "unmanifested_instance_ids": unmanifested_ids,
+        "findings": findings,
+        "active_blockers": active_blockers,
+        "historical_findings": historical_only,
+        "live_fleet_safe": live_safe,
+        "mutation_safe": live_safe and all(
+            inst.get("mutation_safe") for inst in instances
+        )
+        if instances
+        else live_safe,
+        "classification_model": {
+            "exactly_one_process_per_profile": False,
+            "exactly_one_instance_per_client_type": False,
+            "multiple_instances_per_client_type": True,
+            "duplicate_requires": [
+                "live client_instance_id collision",
+                "duplicate namespace worker within one instance",
+                "reused worker/session/generation/process/pid/fencing identity",
+                "cross-instance ownership collision",
+                "unmanifested instance when a manifest is required",
+            ],
+        },
+        "reasons": [f["detail"] for f in active_blockers],
+    }
+
+
+def compare_snapshot_heartbeats(
+    earlier: Mapping[str, Any],
+    later: Mapping[str, Any],
+) -> dict[str, Any]:
+    """Prove heartbeat continuity and stable ownership across two snapshots."""
+    earlier_live = {
+        w.get("worker_identity"): w for w in earlier.get("live_workers") or []
+    }
+    later_live = {
+        w.get("worker_identity"): w for w in later.get("live_workers") or []
+    }
+    shared = sorted(set(earlier_live) & set(later_live))
+    continuity: list[dict[str, Any]] = []
+    stable_ownership = True
+    for wid in shared:
+        a = earlier_live[wid]
+        b = later_live[wid]
+        same_instance = a.get("client_instance_id") == b.get("client_instance_id")
+        same_session = a.get("session_id") == b.get("session_id")
+        same_generation = a.get("generation_id") == b.get("generation_id")
+        hb_advanced_or_equal = True
+        if a.get("last_heartbeat_at") and b.get("last_heartbeat_at"):
+            hb_advanced_or_equal = b["last_heartbeat_at"] >= a["last_heartbeat_at"]
+        if not (same_instance and same_session and same_generation):
+            stable_ownership = False
+        continuity.append(
+            {
+                "worker_identity": wid,
+                "same_client_instance_id": same_instance,
+                "same_session_id": same_session,
+                "same_generation_id": same_generation,
+                "heartbeat_non_decreasing": hb_advanced_or_equal,
+                "earlier_heartbeat": a.get("last_heartbeat_at"),
+                "later_heartbeat": b.get("last_heartbeat_at"),
+            }
+        )
+    return {
+        "shared_live_workers": shared,
+        "continuity": continuity,
+        "stable_ownership": stable_ownership
+        and all(c["heartbeat_non_decreasing"] for c in continuity),
+        "dropped_workers": sorted(set(earlier_live) - set(later_live)),
+        "new_workers": sorted(set(later_live) - set(earlier_live)),
+    }

mcp_worker_identity.py

@@ -301,8 +301,22 @@ CREATE INDEX IF NOT EXISTS idx_worker_session
     ON worker_registrations(session_id, status);
 CREATE INDEX IF NOT EXISTS idx_worker_profile
     ON worker_registrations(profile, status);
+CREATE INDEX IF NOT EXISTS idx_worker_instance
+    ON worker_registrations(client_instance_id, status);
 """
 
+#: #978 optional columns added without rewriting historical rows.
+_SCHEMA_OPTIONAL_COLUMNS: tuple[tuple[str, str], ...] = (
+    ("fleet_run_id", "TEXT"),
+    ("authenticated_account", "TEXT"),
+    ("process_identity", "TEXT"),
+    ("startup_revision", "TEXT"),
+    ("loaded_revision", "TEXT"),
+    ("parity_revision", "TEXT"),
+    ("live_revision", "TEXT"),
+    ("instance_id_provenance", "TEXT"),
+)
+
 
 class WorkerRegistryError(RuntimeError):
     """Raised for registry misuse that is a programming error, not a refusal."""
@@ -634,6 +648,17 @@ class WorkerRegistry:
             conn = self._connect()
             try:
                 conn.executescript(_SCHEMA_SQL)
+                existing = {
+                    row[1]
+                    for row in conn.execute(
+                        "PRAGMA table_info(worker_registrations)"
+                    ).fetchall()
+                }
+                for name, decl in _SCHEMA_OPTIONAL_COLUMNS:
+                    if name not in existing:
+                        conn.execute(
+                            f"ALTER TABLE worker_registrations ADD COLUMN {name} {decl}"
+                        )
                 conn.commit()
             finally:
                 conn.close()
@@ -758,6 +783,14 @@ class WorkerRegistry:
         heartbeat_ttl_seconds: float = DEFAULT_HEARTBEAT_TTL_SECONDS,
         now: datetime | None = None,
         pid_alive_probe=None,
+        fleet_run_id: str | None = None,
+        authenticated_account: str | None = None,
+        process_identity: str | None = None,
+        startup_revision: str | None = None,
+        loaded_revision: str | None = None,
+        parity_revision: str | None = None,
+        live_revision: str | None = None,
+        instance_id_provenance: str | None = None,
     ) -> dict[str, Any]:
         """Atomically register one worker identity.
 
@@ -766,6 +799,10 @@ class WorkerRegistry:
         to mint a different identity and register that instead (AC32). The
         existing registration is returned untouched so the caller can see what
         it collided with.
+
+        #978 also fails closed when a *live* registration already holds the same
+        ``client_instance_id`` for the same namespace: two workers of one
+        namespace cannot share one instance.
         """
         parsed = parse_worker_identity(worker_identity)
         if not parsed["valid"]:
@@ -783,6 +820,9 @@ class WorkerRegistry:
             }
 
         stamp = _ts(now or _utc_now())
+        proc_id = process_identity or (
+            f"pid-{int(pid)}" if pid is not None else None
+        )
         with self._tx() as conn:
             existing = conn.execute(
                 "SELECT * FROM worker_registrations WHERE worker_identity = ?",
@@ -819,6 +859,41 @@ class WorkerRegistry:
                     ),
                 }
 
+            # #978: refuse a second live worker for the same (instance, namespace).
+            if namespace and client_instance_id:
+                peers = conn.execute(
+                    "SELECT * FROM worker_registrations "
+                    "WHERE client_instance_id = ? AND namespace = ? AND status = ?",
+                    (client_instance_id, namespace, STATUS_ACTIVE),
+                ).fetchall()
+                for peer_row in peers:
+                    peer = self._row_to_record(peer_row)
+                    pid_alive = (
+                        pid_alive_probe(peer.get("pid"))
+                        if pid_alive_probe is not None
+                        else None
+                    )
+                    if self.is_live(peer, now=now, pid_alive=pid_alive)["live"]:
+                        return {
+                            "success": False,
+                            "registered": False,
+                            "mutation_performed": False,
+                            "blocker_kind": BLOCKER_CONFLICTING_SESSIONS,
+                            "collision": True,
+                            "collision_kind": "duplicate_namespace_worker",
+                            "existing_registration": _public_record(peer),
+                            "reasons": [
+                                f"client_instance_id {client_instance_id!r} already "
+                                f"has a live worker for namespace {namespace!r} "
+                                f"({peer.get('worker_identity')!r}); #978 fails closed "
+                                "rather than registering a second worker"
+                            ],
+                            "exact_next_action": (
+                                "Stop the extra namespace worker, or use a distinct "
+                                "client_instance_id for a separate application launch."
+                            ),
+                        }
+
             epoch = self._next_epoch(conn, generation_id)
             conn.execute(
                 """
@@ -827,8 +902,11 @@ class WorkerRegistry:
                     generation_id, role, profile, namespace, remote,
                     repository_binding, pid, transport, token_fingerprint,
                     started_at, last_heartbeat_at, heartbeat_ttl_seconds,
-                    fencing_epoch, status
-                ) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)
+                    fencing_epoch, status,
+                    fleet_run_id, authenticated_account, process_identity,
+                    startup_revision, loaded_revision, parity_revision,
+                    live_revision, instance_id_provenance
+                ) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)
                 """,
                 (
                     worker_identity,
@@ -849,6 +927,14 @@ class WorkerRegistry:
                     float(heartbeat_ttl_seconds),
                     epoch,
                     STATUS_ACTIVE,
+                    (fleet_run_id or "").strip() or None,
+                    (authenticated_account or "").strip() or None,
+                    proc_id,
+                    (startup_revision or "").strip() or None,
+                    (loaded_revision or "").strip() or None,
+                    (parity_revision or "").strip() or None,
+                    (live_revision or "").strip() or None,
+                    (instance_id_provenance or "").strip() or None,
                 ),
             )
             row = conn.execute(
@@ -1149,8 +1235,17 @@ def _public_record(record: dict[str, Any]) -> dict[str, Any]:
         "transport": record.get("transport"),
         "started_at": record.get("started_at"),
         "last_heartbeat_at": record.get("last_heartbeat_at"),
+        "heartbeat_ttl_seconds": record.get("heartbeat_ttl_seconds"),
         "fencing_epoch": record.get("fencing_epoch"),
         "status": record.get("status"),
+        "fleet_run_id": record.get("fleet_run_id"),
+        "authenticated_account": record.get("authenticated_account"),
+        "process_identity": record.get("process_identity"),
+        "startup_revision": record.get("startup_revision"),
+        "loaded_revision": record.get("loaded_revision"),
+        "parity_revision": record.get("parity_revision"),
+        "live_revision": record.get("live_revision"),
+        "instance_id_provenance": record.get("instance_id_provenance"),
     }
 
 

task_capability_map.py

@@ -163,6 +163,18 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.read",
         "role": "author",
     },
+    # #978: instance-level fleet identity/health snapshot. gitea.read is the
+    # operation gate; the tool additionally restricts role_kind to
+    # controller|reconciler so author/reviewer/merger cannot use it as a
+    # mutation surface and no unrelated write permission is introduced.
+    "snapshot_instance_fleet": {
+        "permission": "gitea.read",
+        "role": "controller",
+    },
+    "gitea_snapshot_instance_fleet": {
+        "permission": "gitea.read",
+        "role": "controller",
+    },
     # #644: Phase 2 Web Console recovery tasks.
     "clear_stale_binding": {
         "permission": "gitea.read",