refactor(token-meter): merge measurement snapshots (round 1)

docs/core-data-structures/token-meter.md

@@ -1,6 +1,6 @@
 # Token Meter
 
-`@deepseek-ai/dsh-token-meter` exposes detached replay measurements for request pressure and positional surface pricing. Scalar and surface snapshots carry the number of durable events consumed as `logRevision`; consumers compare revisions before making a joint decision.
+`@deepseek-ai/dsh-token-meter` exposes one detached replay snapshot for request pressure and positional surface pricing. `logRevision` is the number of durable events consumed for every field in the measurement.
 
 Source: [`packages/llm/token-meter/src/types.ts`](../../packages/llm/token-meter/src/types.ts)
 
@@ -16,10 +16,14 @@ interface TokenMeasurement {
   readonly surfaceDeltaTokens: number
   /** Non-negative current request-and-response pressure. */
   readonly totalTokens: number
+  /** Total heuristic tokens across the current surface. */
+  readonly surfaceTokens: number
+  /** Current surface nodes in positional head-to-tail order. */
+  readonly nodes: readonly TokenSurfaceNode[]
 }
 ```
 
-`baseline.kind === 'usage'` means the latest successful provider call has the same canonical request envelope. `estimated` means the service priced the complete envelope and surface with its fixed heuristic. A later successful request replaces the earlier anchor; signed `surfaceDeltaTokens` preserves growth and shrinkage relative to a matching anchor.
+`baseline.kind === 'usage'` means the latest successful provider call has the same canonical request envelope. `estimated` means the service priced the complete envelope and surface with its fixed heuristic. A later successful request replaces the earlier anchor; signed `surfaceDeltaTokens` preserves growth and shrinkage relative to a matching anchor. `totalTokens` remains request-and-response pressure, while `surfaceTokens` is the surface-only heuristic total and equals the sum of the node prices.
 
 ## `TokenSurfaceNode`
 
@@ -32,17 +36,4 @@ interface TokenSurfaceNode {
 }
 ```
 
-## `TokenSurfaceMeasurement`
-
-```ts type-equiv
-interface TokenSurfaceMeasurement {
-  /** Number of durable events consumed; equal to the next unread event seq. */
-  readonly logRevision: number
-  /** Total heuristic tokens across the current surface. */
-  readonly totalTokens: number
-  /** Current surface nodes in positional head-to-tail order. */
-  readonly nodes: readonly TokenSurfaceNode[]
-}
-```
-
 Surface order is authoritative; replacement nodes can have higher durable seqs than later positional nodes. The snapshot is immutable and does not grow when the underlying replay fold advances.