diff --git a/src/infospace_bench/budget.py b/src/infospace_bench/budget.py
index 0172f63..90b53f0 100644
--- a/src/infospace_bench/budget.py
+++ b/src/infospace_bench/budget.py
@@ -21,8 +21,10 @@ import yaml
 
 BUDGET_DIR = Path("output/budget")
 PLANS_FILE = BUDGET_DIR / "plans.yaml"
+USAGE_FILE = BUDGET_DIR / "usage.yaml"
 PLAN_RETENTION_DEFAULT = 50
 PLANS_SCHEMA_VERSION = 1
+USAGE_SCHEMA_VERSION = 1
 
 _SNAPSHOT_FINGERPRINT_FIELDS = (
     "stage",
@@ -82,6 +84,162 @@ def read_plan_snapshots(root: str | Path) -> list[dict[str, Any]]:
     return list(payload.get("snapshots") or [])
 
 
+def latest_plan_snapshot_id(root: str | Path) -> str | None:
+    snapshots = read_plan_snapshots(root)
+    if not snapshots:
+        return None
+    return snapshots[-1].get("snapshot_id")
+
+
+def record_run_usage(
+    root: str | Path,
+    workflow_results: list[dict[str, Any]],
+    *,
+    snapshot_id: str | None = None,
+    duration_seconds: float | None = None,
+    started_at: str | None = None,
+    cost_resolver: Any | None = None,
+) -> dict[str, Any]:
+    """Aggregate per-call usage from completed workflow run records.
+
+    ``cost_resolver`` is a callable ``(provider, model, prompt_tokens,
+    completion_tokens) -> float | None`` used to fill ``cost_usd_estimated``
+    when the adapter did not return a cost. Left as ``None`` here; T03
+    wires the rate-table resolver in.
+    """
+    root_path = Path(root)
+    usage_path = root_path / USAGE_FILE
+    usage_path.parent.mkdir(parents=True, exist_ok=True)
+    buckets: dict[tuple, dict[str, Any]] = {}
+    workflow_summaries: list[dict[str, Any]] = []
+    for workflow in workflow_results or []:
+        if not isinstance(workflow, dict):
+            continue
+        workflow_id = str(workflow.get("workflow_id") or "")
+        workflow_summary = {
+            "run_id": workflow.get("run_id"),
+            "workflow_id": workflow_id,
+            "status": workflow.get("status"),
+            "stage_count": len(workflow.get("stages") or []),
+        }
+        workflow_summaries.append(workflow_summary)
+        for stage in workflow.get("stages") or []:
+            if not isinstance(stage, dict):
+                continue
+            provider = str(stage.get("provider") or "")
+            if not provider:
+                continue
+            metadata = stage.get("metadata") or {}
+            model = str(metadata.get("model") or "")
+            usage = metadata.get("usage") or {}
+            prompt_tokens = int(usage.get("prompt_tokens") or 0)
+            completion_tokens = int(usage.get("completion_tokens") or 0)
+            reported_cost = _coerce_float(usage.get("cost"))
+            bucket_key = (workflow_id, str(stage.get("stage_id") or ""), provider, model)
+            bucket = buckets.setdefault(
+                bucket_key,
+                {
+                    "workflow_id": workflow_id,
+                    "stage_id": str(stage.get("stage_id") or ""),
+                    "provider": provider,
+                    "model": model,
+                    "calls": 0,
+                    "prompt_tokens": 0,
+                    "completion_tokens": 0,
+                    "total_tokens": 0,
+                    "cost_usd_known": 0.0,
+                    "cost_usd_estimated": 0.0,
+                    "cost_status": "known" if reported_cost is not None else "unknown",
+                    "cost_estimated_for_calls": 0,
+                },
+            )
+            bucket["calls"] += 1
+            bucket["prompt_tokens"] += prompt_tokens
+            bucket["completion_tokens"] += completion_tokens
+            bucket["total_tokens"] += prompt_tokens + completion_tokens
+            if reported_cost is not None:
+                bucket["cost_usd_known"] = round(bucket["cost_usd_known"] + reported_cost, 6)
+                bucket["cost_status"] = "known"
+            elif cost_resolver is not None:
+                estimated = cost_resolver(provider, model, prompt_tokens, completion_tokens)
+                if estimated is not None:
+                    bucket["cost_usd_estimated"] = round(
+                        bucket["cost_usd_estimated"] + float(estimated), 6
+                    )
+                    bucket["cost_estimated_for_calls"] += 1
+                    if bucket["cost_status"] != "known":
+                        bucket["cost_status"] = "estimated"
+    per_bucket = list(buckets.values())
+    for bucket in per_bucket:
+        if bucket["cost_usd_estimated"] == 0.0 and bucket["cost_estimated_for_calls"] == 0:
+            bucket["cost_usd_estimated"] = None
+    rollup = {
+        "total_calls": sum(b["calls"] for b in per_bucket),
+        "total_prompt_tokens": sum(b["prompt_tokens"] for b in per_bucket),
+        "total_completion_tokens": sum(b["completion_tokens"] for b in per_bucket),
+        "total_tokens": sum(b["total_tokens"] for b in per_bucket),
+        "total_cost_usd_known": round(sum(b["cost_usd_known"] for b in per_bucket), 6),
+        "total_cost_usd_estimated": round(
+            sum(b["cost_usd_estimated"] or 0.0 for b in per_bucket), 6
+        )
+        or None,
+    }
+    completed_at = _now()
+    entry = {
+        "run_index": _next_run_index(usage_path),
+        "started_at": started_at,
+        "completed_at": completed_at,
+        "duration_seconds": duration_seconds,
+        "snapshot_id": snapshot_id,
+        "workflows": workflow_summaries,
+        "rollup": rollup,
+        "per_bucket": per_bucket,
+    }
+    payload = _read_usage(usage_path)
+    runs = list(payload.get("runs") or [])
+    runs.append(entry)
+    _write_usage(
+        usage_path,
+        {"schema_version": USAGE_SCHEMA_VERSION, "runs": runs},
+    )
+    return entry
+
+
+def read_usage_runs(root: str | Path) -> list[dict[str, Any]]:
+    payload = _read_usage(Path(root) / USAGE_FILE)
+    return list(payload.get("runs") or [])
+
+
+def _coerce_float(value: Any) -> float | None:
+    if value is None:
+        return None
+    try:
+        return float(value)
+    except (TypeError, ValueError):
+        return None
+
+
+def _next_run_index(usage_path: Path) -> int:
+    payload = _read_usage(usage_path)
+    return len(payload.get("runs") or []) + 1
+
+
+def _read_usage(path: Path) -> dict[str, Any]:
+    if not path.is_file():
+        return {"schema_version": USAGE_SCHEMA_VERSION, "runs": []}
+    try:
+        data = yaml.safe_load(path.read_text(encoding="utf-8"))
+    except yaml.YAMLError:
+        return {"schema_version": USAGE_SCHEMA_VERSION, "runs": []}
+    if not isinstance(data, dict):
+        return {"schema_version": USAGE_SCHEMA_VERSION, "runs": []}
+    return data
+
+
+def _write_usage(path: Path, payload: dict[str, Any]) -> None:
+    path.write_text(yaml.safe_dump(payload, sort_keys=False), encoding="utf-8")
+
+
 def _build_snapshot(summary: dict[str, Any]) -> dict[str, Any]:
     filters = {
         "stage": summary.get("stage"),
diff --git a/src/infospace_bench/generator.py b/src/infospace_bench/generator.py
index b921aa1..8d30ba4 100644
--- a/src/infospace_bench/generator.py
+++ b/src/infospace_bench/generator.py
@@ -2,11 +2,14 @@ from __future__ import annotations
 
 import hashlib
 import shutil
+import time
 from dataclasses import asdict, dataclass, field
 from datetime import datetime, timezone
 from pathlib import Path
 from typing import Any
 
+_monotonic = time.monotonic
+
 import yaml
 
 from .checks import run_collection_checks
@@ -15,7 +18,11 @@ from .evaluation_io import read_entity_evaluations
 from .history import get_history, read_metrics_file, record_check_results
 from .lifecycle import create_infospace, load_infospace, register_artifact
 from .openrouter import OpenRouterAssistedGenerationAdapter
-from .budget import record_plan_snapshot
+from .budget import (
+    latest_plan_snapshot_id,
+    record_plan_snapshot,
+    record_run_usage,
+)
 from .source_intake import SourceChunk, normalize_source
 from .workflow import (
     AssistedGenerationAdapter,
@@ -343,6 +350,8 @@ def run_generation(
             metrics=status.get("metrics", {}),
         )
 
+    started_wall = datetime.now(timezone.utc)
+    monotonic_start = _monotonic()
     adapter = (
         _adapter_for(provider, model=model, fixture_responses=fixture_responses)
         if workflow_ids
@@ -379,6 +388,15 @@ def run_generation(
         }
     )
     _write_state(root_path, state)
+    if workflow_results:
+        duration_seconds = round(_monotonic() - monotonic_start, 3)
+        record_run_usage(
+            root_path,
+            workflow_results,
+            snapshot_id=latest_plan_snapshot_id(root_path),
+            duration_seconds=duration_seconds,
+            started_at=started_wall.isoformat(),
+        )
     return GenerationRunResult(
         root=str(root_path),
         status="completed",
diff --git a/tests/test_budget_registry.py b/tests/test_budget_registry.py
index 8706d1a..8b3269b 100644
--- a/tests/test_budget_registry.py
+++ b/tests/test_budget_registry.py
@@ -61,6 +61,46 @@ def _write_three_chapter_epub(path: Path) -> None:
             )
 
 
+def _write_minimal_fixture(path: Path) -> None:
+    data = {
+        "responses": [
+            {
+                "stage_id": "summarize-source",
+                "input_artifact_id": "*",
+                "markdown": "# Source Summary\n\nA stub summary.\n",
+            },
+            {
+                "stage_id": "extract-entities",
+                "input_artifact_id": "*",
+                "markdown": (
+                    "# Stub Entity\n\n## Definition\n\nA stub.\n\n## Context\n\nFor a budget test.\n"
+                ),
+            },
+            {
+                "stage_id": "extract-relations",
+                "input_artifact_id": "*",
+                "markdown": (
+                    "# Stub Entity Practices Something\n\n## Subject\n\nStub Entity\n\n"
+                    "## Predicate\n\npractices\n\n## Object\n\nSomething\n\n## Relation Type\n\nsupport\n\n"
+                    "## Evidence\n\nA stub.\n"
+                ),
+            },
+            {
+                "stage_id": "evaluate-entity",
+                "input_artifact_id": "*",
+                "markdown": (
+                    "---\nartifact_id: entity/stub-entity.md\nevaluator: fixture\n"
+                    "evaluated_at: '2026-05-17T00:00:00'\n"
+                    "scores:\n  - name: groundedness\n    value: 4.0\n    max_value: 5.0\n"
+                    "  - name: usefulness\n    value: 4.0\n    max_value: 5.0\n---\n\n"
+                    "# Evaluation: entity/stub-entity.md\n"
+                ),
+            },
+        ]
+    }
+    path.write_text(yaml.safe_dump(data, sort_keys=False), encoding="utf-8")
+
+
 def _build_infospace(tmp_path: Path) -> Path:
     book = tmp_path / "book.epub"
     _write_three_chapter_epub(book)
@@ -144,6 +184,103 @@ def test_plan_snapshot_retention_prunes_old_entries(tmp_path: Path) -> None:
     assert data["pruned_count"] >= 1
 
 
+def test_record_run_usage_aggregates_by_workflow_stage_provider_model(tmp_path: Path) -> None:
+    root = _build_infospace(tmp_path)
+    from infospace_bench.budget import record_run_usage, read_usage_runs
+
+    workflow_results = [
+        {
+            "run_id": "run-1",
+            "workflow_id": "generic-source-entities",
+            "status": "completed",
+            "stages": [
+                {
+                    "stage_id": "extract-entities",
+                    "provider": "openrouter",
+                    "metadata": {
+                        "model": "openai/gpt-4o-mini",
+                        "usage": {"prompt_tokens": 1000, "completion_tokens": 200, "total_tokens": 1200},
+                    },
+                },
+                {
+                    "stage_id": "extract-entities",
+                    "provider": "openrouter",
+                    "metadata": {
+                        "model": "openai/gpt-4o-mini",
+                        "usage": {"prompt_tokens": 800, "completion_tokens": 150, "cost": 0.0012},
+                    },
+                },
+                {"stage_id": "split-entities", "message": "split 3 entities"},
+            ],
+        }
+    ]
+
+    entry = record_run_usage(root, workflow_results, snapshot_id="abc123", duration_seconds=4.2)
+
+    assert entry["rollup"]["total_calls"] == 2
+    assert entry["rollup"]["total_prompt_tokens"] == 1800
+    assert entry["rollup"]["total_completion_tokens"] == 350
+    assert entry["rollup"]["total_cost_usd_known"] == 0.0012
+    assert entry["snapshot_id"] == "abc123"
+    assert entry["duration_seconds"] == 4.2
+    assert len(entry["per_bucket"]) == 1
+    bucket = entry["per_bucket"][0]
+    assert bucket["workflow_id"] == "generic-source-entities"
+    assert bucket["stage_id"] == "extract-entities"
+    assert bucket["provider"] == "openrouter"
+    assert bucket["model"] == "openai/gpt-4o-mini"
+    assert bucket["calls"] == 2
+
+    runs = read_usage_runs(root)
+    assert len(runs) == 1
+    assert runs[0]["run_index"] == 1
+
+
+def test_record_run_usage_handles_fixture_runs_without_aborting(tmp_path: Path) -> None:
+    root = _build_infospace(tmp_path)
+    from infospace_bench.budget import record_run_usage
+
+    workflow_results = [
+        {
+            "run_id": "fix-1",
+            "workflow_id": "generic-source-summary",
+            "stages": [
+                {"stage_id": "summarize-source", "provider": "fixture"},
+                {"stage_id": "summarize-source", "provider": "fixture"},
+            ],
+        }
+    ]
+
+    entry = record_run_usage(root, workflow_results)
+
+    fixture_bucket = next(b for b in entry["per_bucket"] if b["provider"] == "fixture")
+    assert fixture_bucket["calls"] == 2
+    assert fixture_bucket["prompt_tokens"] == 0
+    assert fixture_bucket["cost_status"] == "unknown"
+    assert entry["rollup"]["total_cost_usd_known"] == 0.0
+
+
+def test_run_generation_writes_usage_yaml_with_plan_snapshot_id(tmp_path: Path) -> None:
+    root = _build_infospace(tmp_path)
+    from infospace_bench.budget import USAGE_FILE, read_usage_runs
+    from infospace_bench.generator import run_generation
+
+    fixture = tmp_path / "responses.yaml"
+    _write_minimal_fixture(fixture)
+
+    plan_payload = plan_generation(root)
+    run_generation(root, fixture_responses=fixture)
+
+    runs = read_usage_runs(root)
+    assert (root / USAGE_FILE).is_file()
+    assert len(runs) == 1
+    assert runs[0]["snapshot_id"] == plan_payload["snapshot_id"]
+    assert runs[0]["duration_seconds"] is not None and runs[0]["duration_seconds"] >= 0
+    assert runs[0]["rollup"]["total_calls"] >= 0
+    # Fixture mode runs should not claim any known cost
+    assert runs[0]["rollup"]["total_cost_usd_known"] == 0.0
+
+
 def test_plan_cli_writes_snapshot(tmp_path: Path) -> None:
     root = _build_infospace(tmp_path)
     env = os.environ.copy()
diff --git a/workplans/IB-WP-0019-budget-and-usage-registry.md b/workplans/IB-WP-0019-budget-and-usage-registry.md
index 75e3a5d..bfba44b 100644
--- a/workplans/IB-WP-0019-budget-and-usage-registry.md
+++ b/workplans/IB-WP-0019-budget-and-usage-registry.md
@@ -95,7 +95,7 @@ state_hub_task_id: "7f1a4e0a-c1ad-49f3-aad1-6946de9b1219"
 
 ```task
 id: IB-WP-0019-T02
-status: todo
+status: done
 priority: high
 state_hub_task_id: "a612f8d4-f96d-4fae-9aa6-66a7946414f5"
 ```