diff --git a/.changeset/workflow-column-agent-assignment.md b/.changeset/workflow-column-agent-assignment.md
index b9c7cbc967..8dbc8fb081 100644
--- a/.changeset/workflow-column-agent-assignment.md
+++ b/.changeset/workflow-column-agent-assignment.md
@@ -7,3 +7,5 @@ Add per-column agent assignment for workflow columns, behind the combined `exper
 A workflow column can now name a permanent agent from the registry plus a mode — `defer` (the column agent is the default for work in that column that carries no agent/model settings of its own) or `override` (the column agent supersedes node- and task-level agent/model settings). The binding applies to all session-running work attributable to the column's nodes: custom prompt/gate/script nodes, the execute seam's coding session, and step-execute sessions. Precedence is resolved by one shared `@fusion/core` resolver (`resolveColumnAgentBinding` + `resolveEffectiveAgent`) consumed by every reader, with defer/override expressed as explicit named rules and defer granularity all-or-nothing (an own agent identity OR a complete `modelProvider`+`modelId` pair suppresses the column agent). The binding keys off the node's declared IR column; foreach template nodes inherit the enclosing foreach node's column. A missing/deleted agent at resolution time logs and falls back to normal resolution — a live session is never aborted. The built-in default workflow carries no column agents and stays byte-identical (parity oracle); with either flag off, column agents are inert.
 
 The effective column agent is also the principal for the subsystems that previously assumed the running agent is always `task.assignedAgentId`: action gating (`buildActionGateContext` / `buildPermanentAgentGatingContext`) is computed for the agent actually running; heartbeat serialization honors it in both directions (the execute deferral gate, a second `resumeTaskForAgent` pass that re-dispatches tasks whose effective column agent matches, and a reverse-direction heartbeat-scheduler guard so an `allowParallelExecution=false` column agent never heartbeats concurrently with its own session); and a workflow-definition edit or agent runtimeConfig change that re-keys the column-effective agent/model hot-swaps the running graph session, while an agent deleted mid-session falls back without a restart.
+
+Authoring lands in the workflow editor: the column panel gains a registry-backed per-column agent picker plus a defer/override mode toggle, bound columns are badged on their headers, and a node inside an override column shows that its own executor settings are superseded (so override never reads as a bug). Picker interaction states are explicit — flags off disables the picker with a tooltip naming both required flags, an in-flight fetch disables it, a failed fetch shows an inline error, and a stored `agentId` missing from the registry renders an "Agent not found" warning that preserves the IR until the author clears or replaces it. Agent references are validated at save time: the `POST`/`PATCH` workflow routes reject an unknown `agentId` with a typed 4xx naming the offending column, and binding an agent whose permission policy is broader than the project default requires an explicit `confirmPolicyEscalation` flag so override cannot silently re-key action gates to a more-privileged agent.
diff --git a/docs/workflow-steps.md b/docs/workflow-steps.md
index b093b0723f..763413955d 100644
--- a/docs/workflow-steps.md
+++ b/docs/workflow-steps.md
@@ -61,6 +61,36 @@ FN-5769 evaluated whether those conventions required a `1.1.0` schema bump and r
 
 The `workflowColumns` track introduces **IR v2** (`version: "v2"`), where a workflow additionally defines its own **columns** (`{ id, name, traits: [{ trait, config }] }`), places nodes in columns (`node.column`), and gains `hold`, `split`, and `join` node kinds. Columns become first-class, workflow-defined task state carrying composable **traits** (declarative flags + lifecycle hooks); this generalizes the fixed pipeline + the `gateMode` semantics documented below into per-column trait configuration. v1 graphs still parse and upgrade by synthesizing default-workflow columns. The column/trait model — the trait vocabulary, the substrate/policy line, the transition authority, and the graduation gate — is documented in **`docs/architecture.md` § 9 "Workflow-defined columns & traits"** and the **Concepts** glossary (column, trait, lane, hold node, split/join, default workflow, `transitionPending`). The whole v2 model is gated behind `experimentalFeatures.workflowColumns`; with the flag off, the v1 IR and the quality-gate `WorkflowStep` model below are unchanged.
 
+### Workflow IR v2 — per-column agent assignment
+
+A v2 column can optionally name a **permanent agent** from the agent registry, staffing every card that flows through it once instead of node-by-node or task-by-task. The binding is a first-class optional field on the column (not a trait — traits are board-transition policy; this is execution identity):
+
+```
+{ id: "review", name: "Review", traits: [],
+  agent: { agentId: "agent-001", mode: "defer" | "override" } }
+```
+
+**Binding shape.** `agent.agentId` is a non-empty registry agent id; `agent.mode` is `defer` or `override`. The field is omitted entirely when unset — a column with no `agent` key yields no binding, and the built-in default workflow carries none (it stays byte-identical, the parity oracle). Adding a binding forces the workflow to v2.
+
+**Which column governs.** The binding keys off the node's **declared** IR column (`node.column`), never the task's current board lane. A node with no declared column resolves normally (no column agent), even when other columns carry override bindings.
+
+**`defer` vs `override`.**
+
+- **`defer`** — the column agent is the default *only* when the work carries no agent/model settings of its own. "Own settings" is all-or-nothing: an own agent identity **or** a complete `modelProvider`+`modelId` pair suppresses the column agent entirely. An incomplete model pair (provider with no model id) does **not** count as own settings, so the column agent still wins (matching the executor's both-present model rule). The column agent is never blended with own settings — filling only the missing half would create hybrid identities that are impossible to audit.
+- **`override`** — the column agent supersedes node-level and task-level agent/model settings: identity, model, **and** persona.
+
+**Where it applies.** The effective agent governs all session-running work attributable to the column's nodes: custom prompt/gate/script nodes, the execute seam's coding session, and step-execute sessions. Raw CLI script nodes run no session, so the binding is a no-op there (the skip is audited). Every adoption is logged (`running as column agent '<id>' (<mode>)`) so the audit trail explains who ran and why.
+
+**Foreach template inheritance.** A node inside a `foreach` template subgraph inherits the **enclosing foreach node's** column, unless the template node declares its own `column` (which then wins). Each per-step instance session is attributed to the resolved column agent.
+
+**Principal semantics.** The effective column agent becomes the **principal**, not merely a model source. Action gating is computed for the agent actually running (a security boundary — never `task.assignedAgentId` when an override governs). Heartbeat serialization follows it in both directions: a column agent with `allowParallelExecution=false` is serialized like an assigned agent, the engine re-dispatches tasks whose *effective* column agent matches (not only `assignedAgentId` matches), and the heartbeat scheduler never lets a column agent heartbeat concurrently with its own override session. A workflow-definition edit or agent `runtimeConfig` change that re-keys the effective agent/model hot-swaps a running session, the same way a `task.modelProvider` change does today.
+
+**Missing-agent fallback.** A missing or deleted agent at resolution time logs and falls back to normal resolution — a live session is never aborted because its column agent was deleted mid-flight.
+
+**Flag requirements.** Column agents act only when **both** `experimentalFeatures.workflowColumns` and `experimentalFeatures.workflowGraphExecutor` are on; with either off the binding is inert (config is still stored and round-trips — only execution is gated), and the editor surfaces that the picker is disabled with a tooltip naming both flags.
+
+**Write-time validation.** Saving a workflow validates agent references: an unknown `agentId` is rejected with a typed 4xx naming the column. Binding an agent whose permission policy is broader than the project default requires an explicit policy-escalation confirmation (`confirmPolicyEscalation`) at save time, so override cannot silently re-key action gates to a more-privileged agent.
+
 ### Workflow IR v2 — step inversion (foreach, step-review, parse-steps, code)
 
 The **step-inversion** track makes task *steps* themselves workflow-modelable. Today the engine owns step policy end-to-end (PROMPT.md parsing, per-step review verdicts, RETHINK/REVISE control flow, merge blocking). Step inversion extracts exactly one new substrate capability — *run one step inside a task's session, and reset one step to its baseline* — and exposes everything else as authored graph structure. It is additive to IR v2 and gated by `experimentalFeatures.workflowGraphExecutor`. The default coding workflow is untouched and byte-identical (it keeps its monolithic `execute` seam and is the parity oracle); inversion is opt-in via custom workflows and a new built-in **stepwise coding workflow**.
diff --git a/packages/engine/src/__tests__/executor-column-agent-custom-node.test.ts b/packages/engine/src/__tests__/executor-column-agent-custom-node.test.ts
index c7a854c3d2..38ab4a42fc 100644
--- a/packages/engine/src/__tests__/executor-column-agent-custom-node.test.ts
+++ b/packages/engine/src/__tests__/executor-column-agent-custom-node.test.ts
@@ -144,6 +144,26 @@ describe("runGraphCustomNode column-agent resolution (plan U3)", () => {
     }
   });
 
+  it("override column: bare node adopts the column agent (own-absent cell)", async () => {
+    // override × own-absent: nothing to supersede, the column agent is adopted.
+    const store = createMockStore();
+    store.getTask.mockResolvedValue({ id: "FN-001", worktree: "/tmp/wt", log: [] } as any);
+    const { executor, agentStore } = makeExecutor(store, makeAgent());
+    const captured = spyStep(executor);
+
+    const node = { id: "review", kind: "prompt", column: "review", config: { prompt: "Plain." } };
+    const result = await (executor as any).runGraphCustomNode(node, { id: "FN-001" }, {}, OVERRIDE);
+
+    expect(result.outcome).toBe("success");
+    expect(agentStore.getAgent).toHaveBeenCalledWith("agent-col");
+    expect(captured.step.modelProvider).toBe("anthropic");
+    expect(captured.step.modelId).toBe("claude-col");
+    expect(captured.step.prompt).toContain("I am the senior reviewer.");
+    expect(
+      loggedLines(store).some((l) => l.includes("running as column agent 'agent-col' (override)")),
+    ).toBe(true);
+  });
+
   it("missing column agent in registry → logged, node falls back, step still executes", async () => {
     const store = createMockStore();
     store.getTask.mockResolvedValue({ id: "FN-001", worktree: "/tmp/wt", log: [] } as any);
diff --git a/packages/engine/src/__tests__/executor-column-agent-seams.test.ts b/packages/engine/src/__tests__/executor-column-agent-seams.test.ts
index 981b6cd2e3..08c81ae8aa 100644
--- a/packages/engine/src/__tests__/executor-column-agent-seams.test.ts
+++ b/packages/engine/src/__tests__/executor-column-agent-seams.test.ts
@@ -1,6 +1,64 @@
 // Column-agent coding seams: execute + step-execute sessions (plan U4,
 // R2/R3/R4/R8, KTD-2/KTD-3/KTD-5/KTD-6).
 //
+// ─────────────────────────────────────────────────────────────────────────────
+// SURFACE-ENUMERATION MATRIX AUDIT (plan U7 / FN-5893)
+//
+// The invariant is proven across mode × surface × own-settings. Every cell that
+// matters has at least one assertion in one of the five column-agent test files;
+// this block is the completeness ledger (cell → file → test). `own-present` =
+// node cfg.agentId OR complete task model pair; `own-absent` = bare.
+//
+// resolver = column-agent-resolver.test.ts (core, pure precedence)
+// custom   = executor-column-agent-custom-node.test.ts
+// seams    = executor-column-agent-seams.test.ts (this file)
+// princ    = executor-column-agent-principal.test.ts
+//
+// SURFACE: custom node ───────────────────────────────────────────────────────
+//   override × own-present → custom "override column: node with own cfg.agentId…"
+//   override × own-absent  → custom "override column: bare node adopts the column agent"
+//   defer    × own-present → custom "defer column: node with own cfg.agentId keeps it…" (a)
+//   defer    × own-absent  → custom "defer column: …bare node adopts the column agent" (b)
+//
+// SURFACE: execute seam ──────────────────────────────────────────────────────
+//   override × own-present → seams "override column, task assigned to Y → …X's model"
+//   override × own-absent  → seams "override column, bare task (no own settings) → column agent"
+//   defer    × own-present → seams "defer column, task with complete modelProvider/modelId…"
+//   defer    × own-absent  → seams "defer column, bare task (no own settings) → column agent adopted"
+//
+// SURFACE: step-execute ───────────────────────────────────────────────────────
+//   override × own-present → seams "foreach instance node inherits the foreach's bound column…"
+//   override × own-absent  → seams "step-execute override, bare task → column-agent attribution"
+//   defer    × own-present → seams "defer column with task own complete model pair → assigned attribution"
+//   defer    × own-absent  → seams "step-execute defer, bare task → column-agent attribution adopted"
+//
+// SURFACE: heartbeat-deferred (principal) ─────────────────────────────────────
+//   override × own-present → princ "override column X (allowParallelExecution=false)…defers"
+//                            + princ "resumeTaskForAgent…pass 2 re-dispatches it"
+//   override × own-absent  → princ "two tasks bound to different column agents…" (bare tasks)
+//   defer    × own-present → princ "defer column with task own complete model pair → X NOT effective, pass 2 does not fire"
+//   defer    × own-absent  → resolver "defer × bare → column agent wins" (gate input);
+//                            the deferral gate consumes resolveEffectivePrincipalId, exercised override-side above
+//
+// SURFACE: missing-agent fallback ─────────────────────────────────────────────
+//   custom (override) → custom "missing column agent in registry → logged, node falls back…"
+//   execute seam      → seams "column agent missing from registry at seam time → fallback…"
+//   step-execute      → seams "column agent missing from registry at step-execute seam → fallback…"
+//   restart watcher   → princ "column agent deleted mid-session → no restart storm…fallback (R8)"
+//
+// NO-BINDING (parity / invisibility) ──────────────────────────────────────────
+//   execute seam      → seams characterization "execute seam: …assigned agent, no column-agent log"
+//   step-execute      → seams characterization "step session: attribution falls back to assignedAgentId"
+//   gating principal  → princ "no binding → gating context built for the assigned Y (byte-identical)"
+//   default workflow  → workflow-graph-executor-parity.test.ts "column agent feature is invisible…"
+//
+// Cells deliberately NOT separately pinned: defer × heartbeat × own-absent at the
+// *surface* level — the deferral gate's only column-agent input is the resolver
+// verdict (proven in resolver) routed through resolveEffectivePrincipalId (proven
+// override-side, where the principal differs from assignedAgentId; under defer ×
+// own-absent the principal is still the column agent by the same code path).
+// ─────────────────────────────────────────────────────────────────────────────
+//
 // The graph EXECUTE seam (single coding session) and STEP-EXECUTE seam
 // (StepSessionExecutor per-step sessions) must run as the column agent when the
 // governing seam node's DECLARED column carries a binding. Session identity =
@@ -273,6 +331,26 @@ describe("column-agent coding seams (plan U4)", () => {
       ).toBe(true);
     });
 
+    it("override column, bare task (no own settings) → column agent adopted", async () => {
+      // override × own-absent at the execute seam: the column agent wins
+      // regardless of own settings, and here there are none to begin with.
+      const store = createMockStore();
+      const task = singleSessionTask(); // no assignedAgentId, no model pair
+      store.getTask.mockResolvedValue(task as any);
+      const { executor, agentStore } = makeExecutor(store, { "agent-col": makeColumnAgent() });
+      installTaskDoneAgent();
+
+      await runExecuteSeam(executor, task, "execute-node", OVERRIDE_COL);
+
+      const opts = lastFnAgentOpts();
+      expect(opts.defaultProvider).toBe("anthropic");
+      expect(opts.defaultModelId).toBe("claude-col");
+      expect(agentStore.getAgent).toHaveBeenCalledWith("agent-col");
+      expect(
+        loggedLines(store).some((l) => l.includes("running as column agent 'agent-col' (override)")),
+      ).toBe(true);
+    });
+
     it("column agent missing from registry at seam time → fallback to assignedAgentId path, logged, run proceeds", async () => {
       const store = createMockStore();
       const task = singleSessionTask({ assignedAgentId: "agent-Y" });
@@ -376,6 +454,42 @@ describe("column-agent coding seams (plan U4)", () => {
       expect(agentStore.getAgent).not.toHaveBeenCalledWith("agent-col");
     });
 
+    it("override, bare task (no own settings) → step session carries column-agent attribution", async () => {
+      // override × own-absent at the step-execute seam.
+      const store = createMockStore();
+      const task = singleSessionTask(); // no assignedAgentId, no model pair
+      store.getTask.mockResolvedValue(task as any);
+      const { executor, agentStore } = makeExecutor(store, { "agent-col": makeColumnAgent() });
+      installTaskDoneAgent();
+
+      await runStepSessionSeam(executor, task, "foreach-1#0:step-exec", OVERRIDE_COL);
+
+      const opts = lastStepExecutorOpts();
+      expect(opts.effectiveAgentId).toBe("agent-col");
+      expect(opts.assignedAgentRuntimeConfig).toEqual(makeColumnAgent().runtimeConfig);
+      expect(agentStore.getAgent).toHaveBeenCalledWith("agent-col");
+    });
+
+    it("defer, bare task (no own settings) → step session adopts column-agent attribution", async () => {
+      // defer × own-absent at the step-execute seam: nothing suppresses defer, so
+      // the column agent is adopted.
+      const store = createMockStore();
+      const task = singleSessionTask(); // no assignedAgentId, no model pair
+      store.getTask.mockResolvedValue(task as any);
+      const { executor, agentStore } = makeExecutor(store, { "agent-col": makeColumnAgent() });
+      installTaskDoneAgent();
+
+      await runStepSessionSeam(executor, task, "foreach-1#0:step-exec", DEFER_COL);
+
+      const opts = lastStepExecutorOpts();
+      expect(opts.effectiveAgentId).toBe("agent-col");
+      expect(opts.assignedAgentRuntimeConfig).toEqual(makeColumnAgent().runtimeConfig);
+      expect(agentStore.getAgent).toHaveBeenCalledWith("agent-col");
+      expect(
+        loggedLines(store).some((l) => l.includes("running as column agent 'agent-col' (defer)")),
+      ).toBe(true);
+    });
+
     it("column agent missing from registry at step-execute seam → fallback to assigned-agent attribution, logged", async () => {
       const store = createMockStore();
       const task = singleSessionTask({ assignedAgentId: "agent-Y" });
diff --git a/packages/engine/src/__tests__/workflow-graph-executor-parity.test.ts b/packages/engine/src/__tests__/workflow-graph-executor-parity.test.ts
index 885eac385d..dea42fe0e5 100644
--- a/packages/engine/src/__tests__/workflow-graph-executor-parity.test.ts
+++ b/packages/engine/src/__tests__/workflow-graph-executor-parity.test.ts
@@ -10,7 +10,13 @@
 //   suite `stepwise-workflow-parity.test.ts`. Keep the two concerns separate.
 // ─────────────────────────────────────────────────────────────────────────────
 import { describe, expect, it, vi } from "vitest";
-import type { TaskDetail } from "@fusion/core";
+import type { TaskDetail, WorkflowIrV2 } from "@fusion/core";
+import {
+  BUILTIN_CODING_WORKFLOW_IR,
+  buildWorkflowObservation,
+  buildWorkflowObservationFromTask,
+  compareWorkflowRunObservations,
+} from "@fusion/core";
 
 import { WorkflowGraphExecutor } from "../workflow-graph-executor.js";
 import type { WorkflowLegacySeams } from "../workflow-node-handlers.js";
@@ -123,3 +129,73 @@ describe("WorkflowGraphExecutor interpreter-parity", () => {
     expect(seams.merge).not.toHaveBeenCalled();
   });
 });
+
+// ─────────────────────────────────────────────────────────────────────────────
+// COLUMN-AGENT INVISIBILITY PARITY (plan U7 / R9)
+//
+// The per-column agent feature must be invisible when no column carries a
+// binding: the built-in default workflow synthesizes no `agent` field on any
+// column, and a binding-free run produces observations identical to legacy via
+// the same `compareWorkflowRunObservations` machinery the dual-observe gate uses.
+// This is the byte-identity / parity oracle for the feature being unbound.
+// ─────────────────────────────────────────────────────────────────────────────
+describe("column-agent feature is invisible when unbound (U7 / R9)", () => {
+  it("the default built-in workflow synthesizes NO column agent field on any column", () => {
+    const ir = BUILTIN_CODING_WORKFLOW_IR as WorkflowIrV2;
+    expect(ir.version).toBe("v2");
+    expect(ir.columns.length).toBeGreaterThan(0);
+    for (const col of ir.columns) {
+      // Absent, not `null` and not an explicit default — R9 omission guarantee.
+      expect("agent" in col).toBe(false);
+    }
+  });
+
+  it("a binding-free run yields observations identical to legacy (compareWorkflowRunObservations agrees)", async () => {
+    // Drive the graph executor over the default execute→review→merge sequence and
+    // collect the stage transitions; with zero column bindings, the column-agent
+    // feature contributes nothing, so the interpreter observation must equal the
+    // legacy authoritative observation with no drift.
+    const stages: string[] = [];
+    const seams: WorkflowLegacySeams = {
+      planning: async () => ({ outcome: "success" }),
+      execute: async () => ({ outcome: "success" }),
+      review: async () => ({ outcome: "success" }),
+      merge: async () => ({ outcome: "success" }),
+      schedule: async () => ({ outcome: "success" }),
+    };
+    type BaseSeam = "planning" | "execute" | "review" | "merge" | "schedule";
+    const executor = new WorkflowGraphExecutor({
+      seams,
+      handlers: {
+        prompt: async (node, ctx) => {
+          const seam = String(node.config?.seam) as BaseSeam;
+          stages.push(seam);
+          return seams[seam](ctx.task, ctx.context);
+        },
+      },
+    });
+
+    const result = await executor.run(task, {
+      experimentalFeatures: { workflowGraphExecutor: true },
+    });
+    expect(result.outcome).toBe("success");
+
+    // Legacy authoritative observation: a clean run that lands in `done`/merged.
+    const legacyObs = buildWorkflowObservationFromTask(
+      { column: "done", status: "done", review: { verdict: "approve" } },
+      { columnSequence: ["todo", "in-progress", "in-review", "done"] },
+    );
+    // Interpreter (binding-free) observation assembled from the same run.
+    const interpreterObs = buildWorkflowObservation({
+      stageTransitions: ["triage", "execute", "review", "merge"],
+      terminalColumn: "done",
+      terminalStatus: "done",
+      reviewVerdict: "approve",
+      mergeOutcome: "merged",
+    });
+
+    const report = compareWorkflowRunObservations(legacyObs, interpreterObs);
+    expect(report.agree).toBe(true);
+    expect(report.diffs).toEqual([]);
+  });
+});