diff --git a/README.md b/README.md
index a93ad72..ba79918 100644
--- a/README.md
+++ b/README.md
@@ -85,12 +85,19 @@ graph LR
         REP[Report Agent<br/>Synthesis Only]
     end
 
-    MON -->|"Anomaly context<br/>(full text + schema)"| DIAG
+    MON -->|"DetectedAnomaly<br/>(typed + schema)"| DIAG
     DIAG -->|"DiagnosisReport<br/>(claims + sources + conflicts)"| MON
     MON -->|"DiagnosisReport JSON<br/>(structured, attributed)"| REP
-    REP -->|"IncidentReport<br/>(severity + actions)"| MON
+    REP -->|"IncidentReport<br/>(severity + actions, attributed)"| MON
 ```
 
+The coordinator can also fan out **multiple diagnostic sub-agents in parallel**,
+each seeded with a distinct hypothesis, then merge them (cross-fork
+disagreements become escalated conflicts). This is off by default
+(`agent_diagnostic_forks = 1`); see the
+[fork-diagnostics runbook](docs/fork-diagnostics-runbook.md) for how to enable
+and verify it.
+
 ## Agentic Loop
 
 The core loop is driven by Claude's `stop_reason`. The agent keeps calling tools until it decides it has enough information.
diff --git a/docs/fork-diagnostics-runbook.md b/docs/fork-diagnostics-runbook.md
new file mode 100644
index 0000000..731bbef
--- /dev/null
+++ b/docs/fork-diagnostics-runbook.md
@@ -0,0 +1,169 @@
+# Fork-style parallel diagnostic exploration: manual test runbook
+
+Companion to the fork-diagnostics feature (issue #67). This walks through
+running the coordinator in multi-fork mode, what to expect in the logs and
+audit trail, and how to prove the diagnosis actually fanned out in parallel
+rather than running one agent.
+
+## What the feature does
+
+By default the coordinator runs a single diagnostic sub-agent per cycle
+(`detect -> diagnose -> report`). One agent is a single line of reasoning,
+prone to tunnel vision on an ambiguous anomaly with several plausible causes.
+
+In multi-fork mode the coordinator spawns **N diagnostic sub-agents
+concurrently** from the same detected anomaly, each seeded with a distinct
+hypothesis, then **merges the survivors** into one diagnosis. Forks that reach a
+different `anomaly_type` than the primary (highest-confidence) fork produce a
+cross-fork `ConflictRecord` that is surfaced and escalated, never silently
+resolved.
+
+Fork count is config-gated. Default (`agent_diagnostic_forks = 1`) preserves
+single-agent behavior, so nothing changes until you opt in.
+
+## How to run it locally
+
+Prerequisites (see the main README): Docker Compose stack up, Flink job
+submitted, Java simulator JAR built.
+
+1. Bring up the stack:
+
+   ```
+   docker compose up -d
+   ```
+
+2. Enable fan-out via the environment (the knob is `agent_diagnostic_forks`,
+   overridden with the `STREAMOPS_` prefix). 3 forks is a good demo value; the
+   cap is the number of defined hypotheses (currently 4):
+
+   ```
+   export STREAMOPS_AGENT_DIAGNOSTIC_FORKS=3
+   ```
+
+3. Trigger a cycle. Either inject a scenario end-to-end with the demo runner:
+
+   ```
+   python scripts/demo_scenario.py latency-spike
+   ```
+
+   or run the agent directly for one cycle against whatever the stack is
+   currently emitting:
+
+   ```
+   cd mcp-server
+   STREAMOPS_AGENT_DIAGNOSTIC_FORKS=3 uv run python -m streamops_mcp.agent.main --single-cycle
+   ```
+
+To get the **single-agent baseline** to diff against, run the same command with
+`STREAMOPS_AGENT_DIAGNOSTIC_FORKS=1` (or unset).
+
+## What to expect in the logs
+
+Every line from one cycle shares a correlation id (`cid=cyc-...`, see the
+correlated-logs feature, issue #84). The log format is:
+
+```
+<time> [<logger>] [cid=<correlation-id>] <LEVEL> <message>
+```
+
+In fork mode you will see the fan-out, one spawn line per fork with its
+hypothesis, and the merge:
+
+```
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Fanning out 3 diagnostic forks
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Spawning Diagnostic Agent (hypothesis: Resource saturation: CPU, memory/heap, or GC pressure on the affected component.)
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Spawning Diagnostic Agent (hypothesis: Data-side cause: partition skew, hot keys, or a surge in input volume.)
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Spawning Diagnostic Agent (hypothesis: External dependency: a downstream sink, source, or coordination service degrading.)
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Monitor->Diagnostic handoff validated (type=latency_spike, 412 chars)
+...
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] INFO Claim confidence distribution: 4 HIGH, 2 MEDIUM, 1 LOW, 0 UNSOURCED
+```
+
+If the forks disagree on the root cause, the coordinator logs the cross-fork
+conflict (note the `xf-` conflict id and the `f{i}:` namespaced claim ids), and
+escalation surfaces it:
+
+```
+[streamops-mcp.monitor]     [cid=cyc-a1b2c3d4e5f6] WARNING Coordinator received 1 unresolved conflict(s) from Diagnostic Agent
+[streamops-mcp.monitor]     [cid=cyc-a1b2c3d4e5f6] WARNING Conflict xf-0-1 [cross-fork root-cause disagreement]: claims f0:C01 vs f1:C02
+[streamops-mcp.escalation]  [cid=cyc-a1b2c3d4e5f6] ERROR   Incident '...' carries 1 UNRESOLVED diagnostic conflict(s); forcing review
+```
+
+In a non-interactive run (`--single-cycle`) the human acknowledgment gate has no
+stdin, so it records the conflict for manual review rather than blocking:
+
+```
+[streamops-mcp.escalation] [cid=cyc-a1b2c3d4e5f6] WARNING No human input available for unresolved conflicts on incident ...; logged for manual review
+```
+
+If some forks fail after retries, the survivors are still aggregated:
+
+```
+[streamops-mcp.monitor] [cid=cyc-a1b2c3d4e5f6] WARNING 1 of 3 diagnostic forks failed; aggregating 2 survivor(s)
+```
+
+The cycle only aborts if **every** fork fails.
+
+## What to expect in the audit trail
+
+Each incident is appended to `data/audit/incidents.jsonl` (one JSON object per
+line). The fork run shows more sources and claims than a single-agent run (the
+union across forks, id-namespaced), and any cross-fork disagreement in the
+conflict count:
+
+```json
+{
+  "incident_id": "…",
+  "severity": "MEDIUM",
+  "unresolved_conflict_count": 1,
+  "conflicts_acknowledged": null,
+  "diagnosis": {
+    "sources_consulted": ["query_flink_jobs", "query_prometheus", "query_flink_jobs"],
+    "claim_count": 7,
+    "conflict_count": 1,
+    "tools_used": ["query_flink_jobs", "query_prometheus", "query_kafka_lag"]
+  }
+}
+```
+
+## How to prove it actually forked
+
+1. **Shared correlation id + interleaved spawn lines.** All three
+   `Spawning Diagnostic Agent (hypothesis: ...)` lines share one `cid=` and
+   appear back-to-back *before* any fork completes its investigation. Sequential
+   execution would show fork 0 spawn, then its whole tool loop and completion,
+   *then* fork 1 spawn. Concurrent execution interleaves them. (The unit test
+   `test_forks_run_concurrently_with_distinct_hypotheses` proves this
+   structurally with an `asyncio.Barrier`: if the forks ran sequentially the
+   barrier would never release and the test would time out.)
+
+2. **Distinct hypotheses per fork.** The three spawn lines carry three different
+   hypothesis strings, visible in the logs and in the diagnostic prompt.
+
+3. **Namespaced ids in the merged diagnosis.** The merged claims and sources are
+   prefixed per fork (`f0:`, `f1:`, `f2:`), so the merged report carries every
+   fork's evidence without collision. A single-agent run has no such prefixes.
+
+4. **Cross-fork conflict ids.** Disagreements across forks appear as conflicts
+   with `xf-<primary>-<index>` ids and the topic
+   `cross-fork root-cause disagreement`, distinct from intra-fork conflicts.
+
+## Baseline to diff against
+
+Run the same scenario with `STREAMOPS_AGENT_DIAGNOSTIC_FORKS=1`. You should see:
+
+- a single `Spawning Diagnostic Agent` line with **no** hypothesis suffix,
+- no `Fanning out N diagnostic forks` line,
+- no `f{i}:` id prefixes and no `xf-` conflicts in the diagnosis,
+- a smaller `claim_count` / `sources_consulted` in the audit entry.
+
+That difference (concurrent multi-hypothesis fan-out with a merged, still-fully-
+attributed diagnosis vs a single line of reasoning) is the feature.
+
+## Notes
+
+- The hypotheses are currently a fixed set of generic investigative angles.
+  Deriving them from the specific anomaly and adapting the fork count to
+  ambiguity is tracked in issue #91.
+- Cross-cycle change awareness ("what changed since last cycle") is tracked
+  separately in issue #77.