diff --git a/docs/adr/0026-usage-fact-ledger.md b/docs/adr/0026-usage-fact-ledger.md
new file mode 100644
index 0000000..df8a308
--- /dev/null
+++ b/docs/adr/0026-usage-fact-ledger.md
@@ -0,0 +1,146 @@
+# ADR 0026: Usage Fact Ledger
+
+## Status
+
+Accepted.
+
+## Context
+
+ADR-0022 pins the cost-attribution contract for the platform: token,
+provider-reported cost, run count, and duration are attributed by Organization,
+Project, Run, model, and Provider Connection; "missing provider cost remains
+unknown rather than zero." ADR-0021 scopes usage accounting as operational
+reporting, not payment collection (commercial billing stays deferred).
+
+The implementation today stores this as **one scalar per `AgentRun`**:
+`inputTokens`, `outputTokens`, `costUsd?`, `costSource?`, written once from the
+Claude Agent SDK's `result.total_cost_usd` when the run finishes. This is
+adequate for a single provider-reported model loop, but it cannot represent:
+
+- **External capability consumption** inside a run. PDF→Markdown bundle
+  conversion, audio/video transcription, OCR and similar media transforms are
+  not the main agent loop. They run as side effects of a run, may use a
+  different provider/model, may bill in non-token units (pages, seconds,
+  invocations), and may report cost through a different channel than the
+  OpenRouter gateway. Today there is no row to write that cost to — it would
+  either disappear or silently corrupt the run's single scalar.
+- **Multiple model calls within one run** (e.g. a sub-model invoked by a
+  tool, a gateway-side reroute). The scalar collapses them into one number.
+- **Pricebook derivation** after the fact. With only a final USD figure and no
+  `(provider, model, occurredAt, tokens)` fact, an operator cannot re-derive
+  cost from a price table when the provider did not report it.
+
+Treating each external call as a nested `AgentRun` was considered and
+rejected: `AgentRun` carries lock ownership (ADR-0002), session/provider/role
+binding (ADR-0017), admission/capacity semantics (ADR-0022), and the
+user-visible task boundary. External calls hold none of those. Making them
+`AgentRun`s would pollute run counts, admission, lock semantics, and session
+continuity, and would still not solve non-token metering.
+
+## Decision
+
+Introduce **`UsageFact`** as the single source of truth for billable
+consumption inside an `AgentRun`. An `AgentRun` owns zero or more
+append-only `UsageFact` rows; each row records one billable consumption event:
+
+- `kind` — `model_completion` (the main agent loop) | `external_capability`
+  | `tool_proxy`. The kind set is `OPEN`; new kinds must be surfaced, not
+  silently folded into an existing one.
+- `provider` — e.g. `openrouter`, `mineru`, `openai_whisper`.
+- `model?`, `inputTokens?`, `outputTokens?` — token metering, optional
+  because non-token capabilities have none.
+- `quantity?` + `unit?` — non-token metering (pages, audio_seconds,
+  invocations), coexisting with tokens rather than replacing them.
+- `costUsd?` + `costSource` — `provider_reported` | `pricebook_derived` |
+  `unknown`. `costUsd = null` means **unknown, not zero** (ADR-0022). When the
+  provider reported a cost, `costSource = provider_reported` and that value
+  wins. When only tokens are known, a later pricebook pass may derive
+  `costUsd` with `costSource = pricebook_derived`. When neither is possible,
+  `costSource = unknown` and `costUsd` stays null.
+- `occurredAt` — when the consumption happened; the pricebook derivation
+  depends on this, not on `AgentRun.finishedAt`, because an external
+  capability may complete before the run finishes.
+- `capabilityId?` — for `external_capability` facts, the registered capability
+  id (e.g. `pdf_to_md_bundle`, `audio_video_to_text`).
+- `correlationId?` — external request id for reconciliation / idempotency;
+  not part of the aggregation key.
+
+### Invariants
+
+1. **Append-only.** A `UsageFact` row is never updated or deleted. A cost
+   correction is a new row; the old row stays. `onDelete: Cascade` exists only
+   so a hard run delete (itself not a normal path) cleans up its facts.
+2. **Belongs to exactly one Run; never holds a lock.** A fact is a side-effect
+   ledger of one run, not a sub-run. External capability calls obey the same
+   boundary: their identity is `capabilityId + correlationId`, not `RunId`.
+3. **Missing cost ≠ zero.** Aggregation MUST NOT sum `null` `costUsd` as 0.
+   A run whose facts all have `costUsd = null` is "cost unknown" — reported as
+   `runsWithoutCost`, exactly as the pre-migration `costUsd = null` runs are
+   today. A run with at least one `costUsd`-bearing fact contributes its sum.
+
+### Rollup cache
+
+`AgentRun.costUsd / inputTokens / outputTokens / costSource` columns are kept
+as a **derived rollup cache**, not dropped:
+
+- Existing non-`/usage` readers (slash `/usage`, session detail, integration
+  tests asserting `run.costUsd`) continue to work without code changes for
+  historical runs.
+- On run finish, the writer writes the `UsageFact` row first and then mirrors
+  it onto `AgentRun` as two separate statements, not one transaction. The
+  fact is the truth, so it is written first; the cache is derived, so it is
+  written second. A crash between the two leaves the cache stale, but the
+  usage service re-reads `UsageFact` directly, so staleness is recoverable
+  (and the reverse order would lose the truth, which is not). Keeping the
+  fact insert and the run update in separate statements also avoids holding
+  the `AgentRun` row lock across the FK ShareLock taken by the insert, which
+  deadlocks against concurrent workspace teardown under the cascade path
+  `Organization → Project → AgentRun → UsageFact`.
+- The org/project usage service and the slash `/usage` command read from
+  `UsageFact` directly — they are the canonical aggregation path.
+
+### Migration
+
+A new `UsageFact` table is added. For every existing `AgentRun` with a
+non-null `costUsd` or non-null `inputTokens`/`outputTokens`, the migration
+inserts **one synthetic `model_completion` fact** carrying the run's
+provider, model, tokens, cost, and `costSource`. Its `correlationId` is the
+run id, so the row is identifiable as a backfill artefact. This keeps
+historical reporting correct under the new aggregation path. Pre-migration
+runs with no recorded cost remain `runsWithoutCost` by design, matching
+ADR-0022's "missing cost ≠ zero" rule and the existing migration
+`20260709143000_agent_run_cost_tracking`'s "no backfill" stance for the
+truly unrecorded.
+
+## Consequences
+
+- The billing model now supports external capabilities (PDF→MD, ASR, OCR, …)
+  without per-capability schema changes: a new capability is one new
+  `capabilityId` value and one or more `external_capability` facts.
+- `AgentRun.costUsd` is no longer the truth; it is a convenience cache.
+  Readers that need the truth (cost breakdown, per-capability attribution)
+  must read `UsageFact`. The cache MUST be kept consistent on the write path.
+- The capability registry, pricebook, and any commercial settlement remain
+  `OPEN` and out of pilot scope (ADR-0021). This ADR only pins the ledger
+  shape and invariants.
+- `usage.ts` and `/usage` now perform a join against `UsageFact` rather than a
+  single-table scan of `AgentRun`; the index on `(runId, occurredAt)` and
+  `(provider, model, occurredAt)` keeps the existing org/project/report
+  queries bounded.
+- Cost corrections (e.g. a provider rebills a run) produce a new fact row; the
+  rollup cache must be recomputed. The initial release writes facts once at
+  run finish and does not support post-hoc correction flows — that remains
+  `OPEN`.
+
+## Deferred
+
+- **Capability registry** as a first-class spec entity (`Spec.System.Capability`)
+  with org-scoped enable/disable, input/output contracts, metering schemas,
+  and org-exclusive credentials (ADR-0024 alignment). This ADR only reserves
+  the `capabilityId` field and the `external_capability` fact kind.
+- **Pricebook** — a versioned price table keyed by `(provider, model, unit)`
+  with time validity. Required to actually produce `pricebook_derived` costs;
+  until then, facts without provider-reported cost stay `unknown`.
+- **Post-hoc cost correction flow** — append-only today; correction UI and
+  rollup recompute are `OPEN`.
+- **Commercial billing, invoicing, settlement** — still deferred per ADR-0021.
diff --git a/hub/prisma/migrations/20260718120000_usage_fact_ledger/migration.sql b/hub/prisma/migrations/20260718120000_usage_fact_ledger/migration.sql
new file mode 100644
index 0000000..20f60ed
--- /dev/null
+++ b/hub/prisma/migrations/20260718120000_usage_fact_ledger/migration.sql
@@ -0,0 +1,64 @@
+-- ADR-0026: append-only UsageFact ledger. AgentRun.costUsd/inputTokens/
+-- outputTokens become a derived rollup cache; the truth is in UsageFact.
+
+CREATE TABLE "UsageFact" (
+    "id"            TEXT                   NOT NULL,
+    "runId"         TEXT                   NOT NULL,
+    "occurredAt"    TIMESTAMP(3)           NOT NULL,
+    "kind"          TEXT                   NOT NULL,
+    "provider"      TEXT                   NOT NULL,
+    "model"         TEXT,
+    "inputTokens"   INTEGER,
+    "outputTokens"  INTEGER,
+    "quantity"      DECIMAL(18, 6),
+    "unit"          TEXT,
+    "costUsd"       DECIMAL(18, 8),
+    "costSource"    TEXT                   NOT NULL,
+    "capabilityId"  TEXT,
+    "correlationId" TEXT,
+    "metadata"      JSONB                  NOT NULL,
+    "createdAt"     TIMESTAMP(3)           NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    CONSTRAINT "UsageFact_pkey" PRIMARY KEY ("id")
+);
+
+CREATE INDEX "UsageFact_runId_occurredAt_idx" ON "UsageFact"("runId", "occurredAt");
+CREATE INDEX "UsageFact_runId_kind_idx"       ON "UsageFact"("runId", "kind");
+CREATE INDEX "UsageFact_provider_model_occurredAt_idx"
+  ON "UsageFact"("provider", "model", "occurredAt");
+CREATE INDEX "UsageFact_capabilityId_occurredAt_idx"
+  ON "UsageFact"("capabilityId", "occurredAt");
+
+ALTER TABLE "UsageFact"
+  ADD CONSTRAINT "UsageFact_runId_fkey"
+  FOREIGN KEY ("runId") REFERENCES "AgentRun"("id")
+  ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- Backfill: one synthetic model_completion fact per AgentRun that has any
+-- recorded usage (cost or tokens). correlationId = run id marks these as
+-- backfill artefacts (real facts use an external correlation id or null).
+-- Runs with no recorded usage stay fact-less and remain runsWithoutCost,
+-- matching ADR-0022's "missing cost ≠ zero" rule and the pre-existing
+-- migration 20260709143000_agent_run_cost_tracking's "no backfill for the
+-- truly unrecorded" stance.
+INSERT INTO "UsageFact" (
+  "id", "runId", "occurredAt", "kind", "provider", "model",
+  "inputTokens", "outputTokens", "costUsd", "costSource",
+  "correlationId", "metadata"
+)
+SELECT
+  'usagefact_backfill_' || "AgentRun"."id",
+  "AgentRun"."id",
+  COALESCE("AgentRun"."finishedAt", "AgentRun"."startedAt", CURRENT_TIMESTAMP),
+  'model_completion',
+  "AgentRun"."provider",
+  "AgentRun"."model",
+  "AgentRun"."inputTokens",
+  "AgentRun"."outputTokens",
+  "AgentRun"."costUsd",
+  COALESCE("AgentRun"."costSource", 'unknown'),
+  "AgentRun"."id",
+  '{}'::jsonb
+FROM "AgentRun"
+WHERE "AgentRun"."costUsd" IS NOT NULL
+   OR "AgentRun"."inputTokens" IS NOT NULL
+   OR "AgentRun"."outputTokens" IS NOT NULL;
diff --git a/hub/prisma/schema.prisma b/hub/prisma/schema.prisma
index e5f080d..be3e60d 100644
--- a/hub/prisma/schema.prisma
+++ b/hub/prisma/schema.prisma
@@ -596,9 +596,13 @@ model AgentRun {
   summary           String?
   inputTokens       Int?
   outputTokens      Int?
-  /// Provider/gateway-reported cost in USD. Null means this run has no trusted cost fact.
+  /// ADR-0026: derived rollup cache of UsageFact rows for this run. The truth
+  /// is in UsageFact; this column is convenience for existing readers. Null
+  /// means this run has no trusted cost fact (ADR-0022: missing cost ≠ zero).
   costUsd           Decimal?        @db.Decimal(18, 8)
-  /// Semantic source of costUsd, e.g. provider_reported. Not a pricing-estimate fallback.
+  /// ADR-0026: semantic source of the rolled-up costUsd (provider_reported |
+  /// pricebook_derived | unknown). Mirrors the dominant CostSource of the
+  /// run's facts; not a pricing-estimate fallback.
   costSource        String?
   metadata          Json
   error             String?
@@ -612,6 +616,7 @@ model AgentRun {
   projectLock ProjectAgentLock?
   messages    AgentMessage[]    @relation("runMessages")
   fileChanges AgentFileChange[] @relation("runFileChanges")
+  usageFacts  UsageFact[]       @relation("runUsageFacts")
 
   @@index([projectId, status])
   @@index([projectId, finishedAt])
@@ -817,3 +822,50 @@ model AgentFileChange {
   @@index([projectId])
   @@index([path])
 }
+
+// --- Usage fact ledger (ADR-0026) ----------------------------------------
+
+/// ADR-0026: one billable consumption event inside an AgentRun. Append-only;
+/// the run's AgentRun.costUsd/inputTokens/outputTokens are a derived rollup
+/// of these rows, not the truth. kind=external_capability carries capabilityId
+/// for media transforms (PDF→MD, audio/video→text, …). costUsd=null means
+/// unknown, not zero (ADR-0022). The kind set is OPEN: new kinds must be
+/// surfaced, not silently folded in.
+model UsageFact {
+  id            String   @id @default(cuid())
+  runId         String
+  /// When the consumption happened. Pricebook derivation uses this, not
+  /// AgentRun.finishedAt, because an external capability may finish before
+  /// the run ends.
+  occurredAt    DateTime
+  /// model_completion | external_capability | tool_proxy. OPEN set.
+  kind          String
+  /// e.g. openrouter, mineru, openai_whisper.
+  provider      String
+  model         String?
+  inputTokens   Int?
+  outputTokens  Int?
+  /// Non-token meter (pages, audio_seconds, invocations). Coexists with tokens.
+  quantity      Decimal? @db.Decimal(18, 6)
+  unit          String?
+  /// USD. Null = unknown, NOT zero (ADR-0022). When null, costSource=unknown.
+  costUsd       Decimal? @db.Decimal(18, 8)
+  /// provider_reported | pricebook_derived | unknown. Required even when
+  /// costUsd is null, so a reader can distinguish "reported zero" from
+  /// "no report at all".
+  costSource    String
+  /// For kind=external_capability, the registered capability id
+  /// (e.g. pdf_to_md_bundle, audio_video_to_text). Null for model_completion.
+  capabilityId  String?
+  /// External request id for reconciliation / idempotency. Not an aggregation key.
+  correlationId String?
+  metadata      Json
+  createdAt     DateTime @default(now())
+
+  run AgentRun @relation("runUsageFacts", fields: [runId], references: [id], onDelete: Cascade)
+
+  @@index([runId, occurredAt])
+  @@index([runId, kind])
+  @@index([provider, model, occurredAt])
+  @@index([capabilityId, occurredAt])
+}
diff --git a/hub/src/feishu/slashCommands.ts b/hub/src/feishu/slashCommands.ts
index 2753b10..13ad57d 100644
--- a/hub/src/feishu/slashCommands.ts
+++ b/hub/src/feishu/slashCommands.ts
@@ -92,7 +92,18 @@ export function createSlashCommandRegistry(
           finishedAt: { not: null },
         },
         orderBy: { finishedAt: "asc" },
-        select: { model: true, provider: true, inputTokens: true, outputTokens: true, costUsd: true },
+        select: {
+          usageFacts: {
+            select: {
+              provider: true,
+              model: true,
+              inputTokens: true,
+              outputTokens: true,
+              costUsd: true,
+            },
+            orderBy: { occurredAt: "asc" },
+          },
+        },
       });
       await sendText(rt, chatId, formatUsageReport(runs, scope), sendOptions);
     },
@@ -118,18 +129,24 @@ async function currentRoleSessionIds(
   return sessions.map((session) => session.id);
 }
 
-interface UsageRun {
-  readonly model: string;
-  readonly provider: string;
-  readonly inputTokens: number | null;
-  readonly outputTokens: number | null;
-  readonly costUsd: unknown;
+interface UsageRunWithFacts {
+  readonly usageFacts: readonly {
+    readonly provider: string;
+    readonly model: string | null;
+    readonly inputTokens: number | null;
+    readonly outputTokens: number | null;
+    readonly costUsd: unknown;
+  }[];
 }
 
-function formatUsageReport(runs: readonly UsageRun[], scope: "current" | "project"): string {
+function formatUsageReport(runs: readonly UsageRunWithFacts[], scope: "current" | "project"): string {
   if (runs.length === 0) return `${scope === "current" ? "当前角色会话" : "当前项目"}还没有已结束的 Agent run。`;
+  // Bucket by (fact.provider, fact.model) — ADR-0026: external capabilities
+  // carry their own provider/model and contribute their own meter, so a run
+  // with a main loop + an external call lands in two buckets. A run with no
+  // cost-bearing fact is "unrecorded" (ADR-0022: missing cost ≠ zero).
   const buckets = new Map<string, {
-    provider: string; model: string; runs: number; inputTokens: number; outputTokens: number; costUsd: number;
+    provider: string; model: string; facts: number; inputTokens: number; outputTokens: number; costUsd: number;
   }>();
   let recordedRuns = 0;
   let unrecordedRuns = 0;
@@ -137,21 +154,34 @@ function formatUsageReport(runs: readonly UsageRun[], scope: "current" | "projec
   let totalOutputTokens = 0;
   let totalCostUsd = 0;
   for (const run of runs) {
-    const costUsd = decimalToNumberOrNull(run.costUsd);
-    if (costUsd === null) { unrecordedRuns++; continue; }
+    const facts = run.usageFacts;
+    if (facts.length === 0 || !facts.some((f) => f.costUsd !== null && f.costUsd !== undefined)) {
+      unrecordedRuns++;
+      // Tokens from unrecorded runs still count toward totals (matches pre-0026).
+      for (const f of facts) {
+        totalInputTokens += f.inputTokens ?? 0;
+        totalOutputTokens += f.outputTokens ?? 0;
+      }
+      continue;
+    }
     recordedRuns++;
-    const key = `${run.provider}\u0000${run.model}`;
-    const bucket = buckets.get(key) ?? {
-      provider: run.provider, model: run.model, runs: 0, inputTokens: 0, outputTokens: 0, costUsd: 0,
-    };
-    bucket.runs++;
-    bucket.inputTokens += run.inputTokens ?? 0;
-    bucket.outputTokens += run.outputTokens ?? 0;
-    bucket.costUsd += costUsd;
-    buckets.set(key, bucket);
-    totalInputTokens += run.inputTokens ?? 0;
-    totalOutputTokens += run.outputTokens ?? 0;
-    totalCostUsd += costUsd;
+    for (const f of facts) {
+      const costUsd = decimalToNumberOrNull(f.costUsd);
+      if (costUsd === null) continue;
+      const model = f.model ?? "(unknown model)";
+      const key = `${f.provider}\u0000${model}`;
+      const bucket = buckets.get(key) ?? {
+        provider: f.provider, model, facts: 0, inputTokens: 0, outputTokens: 0, costUsd: 0,
+      };
+      bucket.facts += 1;
+      bucket.inputTokens += f.inputTokens ?? 0;
+      bucket.outputTokens += f.outputTokens ?? 0;
+      bucket.costUsd += costUsd;
+      buckets.set(key, bucket);
+      totalInputTokens += f.inputTokens ?? 0;
+      totalOutputTokens += f.outputTokens ?? 0;
+      totalCostUsd += costUsd;
+    }
   }
   const lines = [
     `${scope === "current" ? "当前角色会话" : "当前项目"}用量`,
@@ -160,7 +190,7 @@ function formatUsageReport(runs: readonly UsageRun[], scope: "current" | "projec
   ];
   if (unrecordedRuns > 0) lines.push(`另有 ${formatInteger(unrecordedRuns)} 个 run 未记录成本。`);
   for (const bucket of buckets.values()) {
-    lines.push(`- ${bucket.provider} / ${bucket.model}: ${formatInteger(bucket.runs)} runs, ${formatUsd(bucket.costUsd)}`);
+    lines.push(`- ${bucket.provider} / ${bucket.model}: ${formatInteger(bucket.facts)} 次, ${formatUsd(bucket.costUsd)}`);
   }
   return lines.join("\n");
 }
diff --git a/hub/src/feishu/trigger.ts b/hub/src/feishu/trigger.ts
index 16fe5ee..f1b2747 100644
--- a/hub/src/feishu/trigger.ts
+++ b/hub/src/feishu/trigger.ts
@@ -604,6 +604,32 @@ export function makeTriggerHandler(deps: TriggerDeps): TriggerHandler {
             data: { metadata: mergeSessionMetadata(session.metadata, metadataPatch) },
           });
         }
+        // ADR-0026: the UsageFact ledger is the truth; AgentRun.costUsd /
+        // inputTokens / outputTokens are a derived rollup cache for existing
+        // readers. We write the fact first, then mirror it onto the run.
+        // They are separate statements (not one transaction) so the AgentRun
+        // row lock is held for the shortest possible window and concurrent
+        // workspace teardown cannot deadlock on the FK ShareLock. A crash
+        // between the two leaves the cache stale, but the cache is derived
+        // (the usage service re-reads facts), so staleness is recoverable;
+        // the reverse order would lose the truth and is unrecoverable.
+        const finishedAt = new Date();
+        const reportedCost = result.costUsd;
+        const costSource = reportedCost !== undefined ? "provider_reported" : "unknown";
+        await deps.prisma.usageFact.create({
+          data: {
+            runId: run.id,
+            occurredAt: finishedAt,
+            kind: "model_completion",
+            provider: providerId,
+            model,
+            inputTokens: result.usage.inputTokens,
+            outputTokens: result.usage.outputTokens,
+            costUsd: reportedCost ?? null,
+            costSource,
+            metadata: {},
+          },
+        });
         await deps.prisma.agentRun.update({
           where: { id: run.id },
           data: {
@@ -618,9 +644,10 @@ export function makeTriggerHandler(deps: TriggerDeps): TriggerHandler {
                     : "FAILED",
             inputTokens: result.usage.inputTokens,
             outputTokens: result.usage.outputTokens,
-            ...(result.costUsd !== undefined ? { costUsd: result.costUsd, costSource: "provider_reported" } : {}),
+            costUsd: reportedCost ?? null,
+            costSource,
             error: result.error ?? null,
-            finishedAt: new Date(),
+            finishedAt,
           },
         });
         await writeAudit(deps.prisma, {
diff --git a/hub/src/org/sessions.ts b/hub/src/org/sessions.ts
index 342c1f0..22c6966 100644
--- a/hub/src/org/sessions.ts
+++ b/hub/src/org/sessions.ts
@@ -73,9 +73,28 @@ export async function getSessionDetail(
           inputTokens: true,
           outputTokens: true,
           costUsd: true,
+          costSource: true,
           startedAt: true,
           finishedAt: true,
           error: true,
+          usageFacts: {
+            select: {
+              id: true,
+              occurredAt: true,
+              kind: true,
+              provider: true,
+              model: true,
+              inputTokens: true,
+              outputTokens: true,
+              quantity: true,
+              unit: true,
+              costUsd: true,
+              costSource: true,
+              capabilityId: true,
+              correlationId: true,
+            },
+            orderBy: { occurredAt: "asc" },
+          },
         },
         orderBy: { startedAt: "desc" },
         take: 100,
@@ -106,9 +125,25 @@ export async function getSessionDetail(
       inputTokens: r.inputTokens,
       outputTokens: r.outputTokens,
       costUsd: r.costUsd === null ? null : Number(r.costUsd),
+      costSource: r.costSource,
       startedAt: r.startedAt.toISOString(),
       finishedAt: r.finishedAt?.toISOString() ?? null,
       error: r.error,
+      usageFacts: r.usageFacts.map((f) => ({
+        id: f.id,
+        occurredAt: f.occurredAt.toISOString(),
+        kind: f.kind,
+        provider: f.provider,
+        model: f.model,
+        inputTokens: f.inputTokens,
+        outputTokens: f.outputTokens,
+        quantity: f.quantity === null ? null : Number(f.quantity),
+        unit: f.unit,
+        costUsd: f.costUsd === null ? null : Number(f.costUsd),
+        costSource: f.costSource,
+        capabilityId: f.capabilityId,
+        correlationId: f.correlationId,
+      })),
     })),
   };
 }
diff --git a/hub/src/org/usage.ts b/hub/src/org/usage.ts
index ea32d69..41f2b5e 100644
--- a/hub/src/org/usage.ts
+++ b/hub/src/org/usage.ts
@@ -1,8 +1,14 @@
 /**
- * Org / project usage rollups from AgentRun cost facts (ADR-0021).
+ * Org / project usage rollups from the UsageFact ledger (ADR-0021, ADR-0026).
  * Operational usage accounting, not payment collection. Organizations may use
  * either their own provider credentials or a distinct platform-managed
  * connection; commercial billing remains outside the pilot scope.
+ *
+ * The truth is in `UsageFact`; `AgentRun.costUsd / inputTokens / outputTokens`
+ * are a derived rollup cache. This service reads `UsageFact` directly so that
+ * external-capability consumption (PDF→MD, ASR, …) is attributed correctly,
+ * not just the main model loop. A run with no cost-bearing fact is
+ * `runsWithoutCost` — ADR-0022: missing cost ≠ zero.
  */
 import type { Prisma, PrismaClient } from "@prisma/client";
 
@@ -32,6 +38,53 @@ export interface UsageReport {
   };
 }
 
+type FactRow = {
+  readonly inputTokens: number | null;
+  readonly outputTokens: number | null;
+  readonly costUsd: unknown;
+};
+
+type RunWithFacts = {
+  readonly projectId: string;
+  readonly usageFacts: readonly FactRow[];
+};
+
+/** A run is "recorded with cost" if any of its facts carries a known costUsd. */
+function runHasRecordedCost(facts: readonly FactRow[]): boolean {
+  return facts.some((f) => f.costUsd !== null && f.costUsd !== undefined);
+}
+
+/** Decimal→number for Prisma Decimal; null/undefined → null. */
+function factCostUsdToNumber(value: unknown): number | null {
+  if (value === null || value === undefined) return null;
+  const n = typeof value === "number" ? value : Number(value);
+  return Number.isFinite(n) ? n : null;
+}
+
+interface RunRollup {
+  readonly hasCost: boolean;
+  readonly inputTokens: number;
+  readonly outputTokens: number;
+  readonly costUsd: number | null;
+}
+
+function rollupRun(facts: readonly FactRow[]): RunRollup {
+  let inputTokens = 0;
+  let outputTokens = 0;
+  let costUsd: number | null = null;
+  let hasCost = false;
+  for (const f of facts) {
+    inputTokens += f.inputTokens ?? 0;
+    outputTokens += f.outputTokens ?? 0;
+    const c = factCostUsdToNumber(f.costUsd);
+    if (c !== null) {
+      hasCost = true;
+      costUsd = (costUsd ?? 0) + c;
+    }
+  }
+  return { hasCost, inputTokens, outputTokens, costUsd };
+}
+
 export async function getOrgUsage(
   prisma: PrismaClient,
   input: {
@@ -54,8 +107,9 @@ export async function getOrgUsage(
     return emptyReport(input.from, input.to);
   }
 
+  const projectIds = projects.map((p) => p.id);
   const runWhere: Prisma.AgentRunWhereInput = {
-    projectId: { in: projects.map((p) => p.id) },
+    projectId: { in: projectIds },
     ...(input.from !== undefined || input.to !== undefined
       ? {
           startedAt: {
@@ -66,20 +120,25 @@ export async function getOrgUsage(
       : {}),
   };
 
+  // Date range filters by run.startedAt, matching the pre-ADR-0026 semantics:
+  // a run is in or out of the window based on when it started, and all of its
+  // facts come along. Filtering facts by occurredAt independently would let a
+  // run contribute partial cost to a window it doesn't belong to.
   const runs = await prisma.agentRun.findMany({
     where: runWhere,
     select: {
       projectId: true,
-      inputTokens: true,
-      outputTokens: true,
-      costUsd: true,
+      usageFacts: {
+        select: { inputTokens: true, outputTokens: true, costUsd: true },
+        orderBy: { occurredAt: "asc" },
+      },
     },
   });
 
   type MutableRow = {
-    projectId: string;
-    projectName: string;
-    folderId: string | null;
+    readonly projectId: string;
+    readonly projectName: string;
+    readonly folderId: string | null;
     runCount: number;
     runsWithCost: number;
     runsWithoutCost: number;
@@ -103,22 +162,33 @@ export async function getOrgUsage(
     });
   }
 
-  for (const run of runs) {
+  for (const run of runs as readonly RunWithFacts[]) {
     const row = byProject.get(run.projectId);
     if (row === undefined) continue;
+    const roll = rollupRun(run.usageFacts);
     row.runCount += 1;
-    row.inputTokens += run.inputTokens ?? 0;
-    row.outputTokens += run.outputTokens ?? 0;
-    if (run.costUsd === null) {
-      row.runsWithoutCost += 1;
-    } else {
+    if (roll.hasCost) {
       row.runsWithCost += 1;
-      const cost = Number(run.costUsd);
-      row.costUsd = (row.costUsd ?? 0) + cost;
+      row.costUsd = (row.costUsd ?? 0) + (roll.costUsd ?? 0);
+    } else {
+      row.runsWithoutCost += 1;
     }
+    row.inputTokens += roll.inputTokens;
+    row.outputTokens += roll.outputTokens;
   }
 
-  const projectsOut: ProjectUsageRow[] = [...byProject.values()];
+  const projectsOut: ProjectUsageRow[] = [...byProject.values()].map((r) => ({
+    projectId: r.projectId,
+    projectName: r.projectName,
+    folderId: r.folderId,
+    runCount: r.runCount,
+    runsWithCost: r.runsWithCost,
+    runsWithoutCost: r.runsWithoutCost,
+    inputTokens: r.inputTokens,
+    outputTokens: r.outputTokens,
+    costUsd: r.costUsd,
+  }));
+
   let runCount = 0;
   let runsWithCost = 0;
   let runsWithoutCost = 0;
diff --git a/hub/test/integration/usage.test.ts b/hub/test/integration/usage.test.ts
new file mode 100644
index 0000000..3e226de
--- /dev/null
+++ b/hub/test/integration/usage.test.ts
@@ -0,0 +1,191 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { prisma, resetDb, seedTestOrganization, DEFAULT_ORG_ID } from "./helpers.js";
+import { getOrgUsage, getProjectUsage } from "../../src/org/usage.js";
+
+/**
+ * ADR-0026: org/project usage rolls up from the UsageFact ledger, not from the
+ * AgentRun scalar cache. These tests pin the fact-based aggregation contract:
+ *   - a run with a cost-bearing fact → runsWithCost, costUsd summed
+ *   - a run whose facts all have null costUsd → runsWithoutCost (≠ zero)
+ *   - non-token meter (quantity/unit) is stored but does not corrupt token sums
+ *   - multiple facts per run (main loop + external capability) are summed together
+ *   - the AgentRun rollup cache is NOT consulted by getOrgUsage
+ */
+describe("usage rollup from UsageFact (ADR-0026)", () => {
+  beforeEach(async () => {
+    await resetDb();
+    await seedTestOrganization();
+  });
+
+  async function seedRun(opts: {
+    readonly projectId: string;
+    readonly projectName: string;
+    readonly folderId?: string;
+    readonly facts: ReadonlyArray<{
+      readonly kind?: string;
+      readonly provider?: string;
+      readonly model?: string;
+      readonly inputTokens?: number;
+      readonly outputTokens?: number;
+      readonly costUsd?: number | null;
+      readonly costSource?: string;
+      readonly capabilityId?: string;
+      readonly quantity?: number | null;
+      readonly unit?: string | null;
+    }>;
+  }): Promise<void> {
+    const project = await prisma.project.create({
+      data: {
+        id: opts.projectId,
+        organizationId: DEFAULT_ORG_ID,
+        name: opts.projectName,
+        workspaceDir: `/tmp/test-${opts.projectId}`,
+        ...(opts.folderId !== undefined ? { folderId: opts.folderId } : {}),
+      },
+    });
+    const startedAt = new Date("2026-07-18T10:00:00Z");
+    const finishedAt = new Date("2026-07-18T10:05:00Z");
+    const run = await prisma.agentRun.create({
+      data: {
+        projectId: project.id,
+        entrypoint: "FEISHU",
+        provider: "openrouter",
+        model: "mock-model",
+        metadata: {},
+        status: "COMPLETED",
+        prompt: "test",
+        startedAt,
+        finishedAt,
+        // Deliberately set the rollup cache to values that differ from the
+        // facts, to prove getOrgUsage reads facts, not the cache.
+        inputTokens: 999,
+        outputTokens: 999,
+        costUsd: 999,
+        costSource: "provider_reported",
+      },
+    });
+    for (const [i, f] of opts.facts.entries()) {
+      await prisma.usageFact.create({
+        data: {
+          runId: run.id,
+          occurredAt: new Date(startedAt.getTime() + i * 1000),
+          kind: f.kind ?? "model_completion",
+          provider: f.provider ?? "openrouter",
+          model: f.model ?? "mock-model",
+          inputTokens: f.inputTokens ?? null,
+          outputTokens: f.outputTokens ?? null,
+          costUsd: f.costUsd ?? null,
+          costSource: f.costSource ?? (f.costUsd !== undefined && f.costUsd !== null ? "provider_reported" : "unknown"),
+          capabilityId: f.capabilityId ?? null,
+          quantity: f.quantity ?? null,
+          unit: f.unit ?? null,
+          metadata: {},
+        },
+      });
+    }
+  }
+
+  it("sums cost and tokens from facts, ignoring the AgentRun rollup cache", async () => {
+    await seedRun({
+      projectId: "proj-a",
+      projectName: "A",
+      facts: [{ inputTokens: 10, outputTokens: 5, costUsd: 0.0023 }],
+    });
+    await seedRun({
+      projectId: "proj-b",
+      projectName: "B",
+      facts: [{ inputTokens: 20, outputTokens: 10, costUsd: 0.01 }],
+    });
+
+    const report = await getOrgUsage(prisma, { organizationId: DEFAULT_ORG_ID });
+
+    expect(report.totals.runCount).toBe(2);
+    expect(report.totals.runsWithCost).toBe(2);
+    expect(report.totals.runsWithoutCost).toBe(0);
+    expect(report.totals.inputTokens).toBe(30);
+    expect(report.totals.outputTokens).toBe(15);
+    expect(report.totals.costUsd).toBeCloseTo(0.0123, 8);
+  });
+
+  it("treats a run with only null-cost facts as runsWithoutCost, never zero", async () => {
+    await seedRun({
+      projectId: "proj-unknown",
+      projectName: "Unknown",
+      facts: [{ inputTokens: 7, outputTokens: 3, costUsd: null, costSource: "unknown" }],
+    });
+    await seedRun({
+      projectId: "proj-known",
+      projectName: "Known",
+      facts: [{ inputTokens: 4, outputTokens: 2, costUsd: 0.05 }],
+    });
+
+    const report = await getOrgUsage(prisma, { organizationId: DEFAULT_ORG_ID });
+
+    expect(report.totals.runCount).toBe(2);
+    expect(report.totals.runsWithCost).toBe(1);
+    expect(report.totals.runsWithoutCost).toBe(1);
+    // The unknown-cost run still contributes its tokens.
+    expect(report.totals.inputTokens).toBe(11);
+    expect(report.totals.outputTokens).toBe(5);
+    // And its cost is NOT counted as zero — only the known cost is summed.
+    expect(report.totals.costUsd).toBeCloseTo(0.05, 8);
+  });
+
+  it("sums multiple facts per run (main loop + external capability)", async () => {
+    await seedRun({
+      projectId: "proj-multi",
+      projectName: "Multi",
+      facts: [
+        { kind: "model_completion", inputTokens: 100, outputTokens: 50, costUsd: 0.02 },
+        {
+          kind: "external_capability",
+          provider: "mineru",
+          model: null,
+          inputTokens: null,
+          outputTokens: null,
+          costUsd: 0.015,
+          costSource: "provider_reported",
+          capabilityId: "pdf_to_md_bundle",
+          quantity: 12,
+          unit: "pages",
+        },
+      ],
+    });
+
+    const report = await getOrgUsage(prisma, { organizationId: DEFAULT_ORG_ID });
+    expect(report.totals.runCount).toBe(1);
+    expect(report.totals.runsWithCost).toBe(1);
+    expect(report.totals.inputTokens).toBe(100);
+    expect(report.totals.outputTokens).toBe(50);
+    expect(report.totals.costUsd).toBeCloseTo(0.035, 8);
+  });
+
+  it("a run with no facts at all is runsWithoutCost and contributes nothing", async () => {
+    await seedRun({ projectId: "proj-empty", projectName: "Empty", facts: [] });
+
+    const report = await getOrgUsage(prisma, { organizationId: DEFAULT_ORG_ID });
+    expect(report.totals.runCount).toBe(1);
+    expect(report.totals.runsWithCost).toBe(0);
+    expect(report.totals.runsWithoutCost).toBe(1);
+    expect(report.totals.inputTokens).toBe(0);
+    expect(report.totals.outputTokens).toBe(0);
+    expect(report.totals.costUsd).toBeNull();
+  });
+
+  it("getProjectUsage returns just that project's row", async () => {
+    await seedRun({ projectId: "proj-x", projectName: "X", facts: [{ costUsd: 0.1, inputTokens: 1, outputTokens: 1 }] });
+    await seedRun({ projectId: "proj-y", projectName: "Y", facts: [{ costUsd: 0.2, inputTokens: 2, outputTokens: 2 }] });
+
+    const row = await getProjectUsage(prisma, { organizationId: DEFAULT_ORG_ID, projectId: "proj-x" });
+    expect(row.projectId).toBe("proj-x");
+    expect(row.runCount).toBe(1);
+    expect(row.costUsd).toBeCloseTo(0.1, 8);
+  });
+
+  it("returns an empty report for an org with no projects", async () => {
+    const report = await getOrgUsage(prisma, { organizationId: DEFAULT_ORG_ID });
+    expect(report.projects).toHaveLength(0);
+    expect(report.totals.runCount).toBe(0);
+    expect(report.totals.costUsd).toBeNull();
+  });
+});
diff --git a/hub/test/unit/feishu-reactions.test.ts b/hub/test/unit/feishu-reactions.test.ts
index 1583030..4d52fde 100644
--- a/hub/test/unit/feishu-reactions.test.ts
+++ b/hub/test/unit/feishu-reactions.test.ts
@@ -290,6 +290,9 @@ function mockPrisma(): PrismaClient {
       findUnique: vi.fn(async () => null),
       update: vi.fn(async () => ({ id: "run-1" })),
     },
+    usageFact: {
+      create: vi.fn(async () => ({ id: "fact-1" })),
+    },
     projectAgentLock: {
       findUnique: vi.fn(async () => (lock === null ? null : { runId: lock.runId })),
       create: vi.fn(async (args: { data: { projectId: string; runId: string } }) => {
diff --git a/spec/Spec/System.lean b/spec/Spec/System.lean
index fc8695a..917f114 100644
--- a/spec/Spec/System.lean
+++ b/spec/Spec/System.lean
@@ -10,6 +10,7 @@ import Spec.System.Agent.Run
 import Spec.System.Agent.AgentRole
 import Spec.System.Agent.Memory
 import Spec.System.Agent.AgentSurface
+import Spec.System.Agent.Usage
 import Spec.System.Lock
 import Spec.System.Permission
 import Spec.System.PermissionGrant
@@ -39,11 +40,14 @@ likec4 已画出结构;这里补语义:
 - `Memory` —— 按需上下文:锚点类别(ADR-0003)+ MCP 工具按 run/project 上下文授权。
 - `AgentSurface` —— agent 执行面被 run 的工作区所界定(ADR-0018);与 Lock 正交——
   Lock 限定并发,Surface 限定波及面。机制 OPEN。
+- `Usage` —— Run 内 append-only 用量计量事实账本(ADR-0026);主模型 completion、
+  外部能力调用、代理网关旁路共用同一账本。fact 不持锁、不跨 run;`costUsd = none`
+  表示未知而非零(ADR-0022)。Run 上的 cost/token 标量是其 rollup cache。
 - `Permission` —— read⊂edit⊂manage 角色体系、能力推导、单调性;force-release 在格外。
 - `PermissionGrant` —— grant(resource×principal×role)与 settings(六 policy 旋钮)
   (ADR-0004);组合规则 OPEN。
 - `Audit` —— customer Project/Run 审计从简(内容 OPEN);Platform Audit 由
   `PlatformAdministration` 独立承载。
 
-标识符见 `Spec.Prelude`。决策出处:ADR-0001..0004, 0018, 0020..0024。
+标识符见 `Spec.Prelude`。决策出处:ADR-0001..0004, 0018, 0020..0026。
 -/
diff --git a/spec/Spec/System/Agent/Usage.lean b/spec/Spec/System/Agent/Usage.lean
new file mode 100644
index 0000000..64ed69a
--- /dev/null
+++ b/spec/Spec/System/Agent/Usage.lean
@@ -0,0 +1,92 @@
+import Spec.Prelude
+
+/-!
+# Usage —— Run 内用量计量事实账本(ADR-0026)
+
+一次 `AgentRun` 内可能产生**多条**可计费消耗:主模型 completion、外部能力调用
+(PDF→MD bundle、音视频转写等)、或代理网关侧旁路调用。这些消耗**不**是子 Run——
+它们不持项目锁、不占 session 语义、不复用 `AgentRun` 状态机。它们是 Run 内的
+append-only **计量事实**(`UsageFact`)。
+
+`AgentRun` 上的 cost/token 标量是 facts 的派生 rollup cache,不是真相来源;真相在
+`UsageFact` 行。这一层抽象让"主模型"与"外部能力"两类消耗共享同一账本,而非给后者
+各开一种特化字段或 nested Run。
+
+核心不变式(`PINNED`, ADR-0022 + ADR-0026):
+
+- **append-only** —— fact 一旦写入只读不更不删;`costUsd` 修正走新 fact,不改旧行。
+- **`costUsd = none` 表示"未知",不是"零成本"** —— ADR-0022:missing provider cost
+  remains unknown rather than zero。聚合时不得把 none 当 0 求和。
+- **fact 不持锁、不跨 run** —— 它是 Run 内的副作用账本,不是又一次 `@bot` 生命周期。
+  外部能力调用亦同:它的语义边界是 `capabilityId` + `correlationId`,不是 `RunId`。
+- **价目回算是派生** —— `costSource = pricebookDerived` 时,`costUsd` 由
+  `occurredAt × (provider, model)` 查价目表派生;provider 实报(`providerReported`)
+  优先于派生。无价目可查时 `costSource = unknown`,`costUsd = none`。
+
+外部能力(capability)注册表、价目表(pricebook)、商业结算均 `OPEN`,pilot 不做
+(ADR-0021 仍 defer commercial billing)。本模块只 pin **账本结构与不变式**。
+-/
+
+namespace Spec.System.Agent
+
+variable (I : Identifiers) (Time Cost Quantity : Type)
+
+/-- 计量事实类型(`PINNED`, ADR-0026)。集合完整性 `OPEN`——新增 kind 须 surface,
+不得静默把外部消耗塞进既有 kind。 -/
+inductive UsageFactKind where
+  /-- 主 agent loop 的模型 completion(`PINNED`)。 -/
+  | modelCompletion
+  /-- 外部能力调用(`PINNED`;如 pdf_to_md_bundle、audio_video_to_text)。 -/
+  | externalCapability
+  /-- 代理网关侧旁路调用(`PINNED`;非主 loop 的模型调用,如嵌入工具内的子请求)。 -/
+  | toolProxy
+
+/-- 成本来源(`PINNED`, ADR-0026)。优先级:provider 实报 > 价目派生 > unknown。 -/
+inductive CostSource where
+  /-- provider/gateway 实报(`PINNED`)。 -/
+  | providerReported
+  /-- 用 `occurredAt × (provider, model)` 价目表派生(`PINNED`)。 -/
+  | pricebookDerived
+  /-- 缺失,而非零(`PINNED`;ADR-0022 missing cost ≠ zero)。 -/
+  | unknown
+
+/-- 一次可计费消耗的计量事实(`PINNED`, ADR-0026)。append-only;一次 run ≥0 条。
+
+字段分两组:**归属与时间**(run/occurredAt/kind)用于聚合与价目回算;
+**计量与成本**(tokens/quantity/unit/costUsd/costSource)用于账目本身。
+非 token 计量(页/秒/次)走 `quantity + unit`,与 token 并存而非取代。 -/
+structure UsageFact where
+  /-- 所属 run(`PINNED`;fact 不跨 run,fact 不持锁,ADR-0026)。 -/
+  run : I.RunId
+  /-- 消耗发生时刻(`PINNED`);价目回算依赖此字段而非 run.finishedAt,
+  因为外部能力可能早于 run 结束。 -/
+  occurredAt : Time
+  /-- 事实类型(`PINNED`, ADR-0026)。 -/
+  kind : UsageFactKind
+  /-- provider 标识(`PINNED`;如 openrouter、mineru、openai_whisper)。 -/
+  provider : String
+  /-- 模型标识(`OPEN`;非模型计费可为 none)。 -/
+  model : Option String
+  /-- 输入 tokens(`OPEN`;非 token 计量可为 none)。 -/
+  inputTokens : Option Nat
+  /-- 输出 tokens(`OPEN`)。 -/
+  outputTokens : Option Nat
+  /-- 非 token 计量数值(`OPEN`;如页数、音频秒数)。与 tokens 并存。 -/
+  quantity : Option Quantity
+  /-- 计量单位(`OPEN`;如 "pages"、"audio_seconds"、"invocations")。 -/
+  unit : Option String
+  /-- 成本(`PINNED`;none = 未知,非零,ADR-0022)。 -/
+  costUsd : Option Cost
+  /-- 成本来源(`PINNED`;costUsd ≠ none 时必填,costUsd = none 时为 `unknown`)。 -/
+  costSource : CostSource
+  /-- 外部能力标识(`OPEN`;kind = externalCapability 时填,如 pdf_to_md_bundle)。 -/
+  capabilityId : Option String
+  /-- 外部请求关联 id(`OPEN`;对账/幂等用,不参与聚合)。 -/
+  correlationId : Option String
+
+/-- Fact 的成本是否**已知**(`PINNED`, ADR-0026)。聚合 rollup 时,只对已知成本求和;
+未知成本的 fact 不贡献 0,而是让汇总保持未知(若所有 fact 均未知)或部分未知。 -/
+def UsageFact.HasKnownCost (fact : UsageFact I Time Cost Quantity) : Prop :=
+  fact.costUsd ≠ none
+
+end Spec.System.Agent