fix(handlers): address code-review feedback on lines_of_code semantics

- handleSessionError: read sessionTotals before deleting, so the AGENT_NAME
  attribute on the error span is actually populated (pre-existing bug the
  reviewer surfaced in this diff's adjacent block).
- handleSessionDiff: write sessionDiffTotals through setBoundedMap, matching
  the repo convention for sessionTotals / sessionSpans / pendingToolSpans
  (MAX_PENDING = 500 cap against unbounded growth).
- otel.ts / README.md: spell out the counter's "sums gross additions across
  non-revert deltas" semantics and direct readers to lines_of_code.total as
  the authoritative live cumulative; note that intra-message reverts are
  not captured.

Author: Jeevan1351

README.md

@@ -31,8 +31,8 @@ An [opencode](https://opencode.ai) plugin that exports telemetry via OpenTelemet
 | `opencode.session.count` | Counter | Incremented on each `session.created` event |
 | `opencode.token.usage` | Counter | Per token type: `input`, `output`, `reasoning`, `cacheRead`, `cacheCreation` |
 | `opencode.cost.usage` | Counter | USD cost per completed assistant message |
-| `opencode.lines_of_code.count` | Counter | Net lines added/removed in the session. The handler emits only the positive delta since the previous `session.diff`, so summing the counter yields the true cumulative total without double-counting. |
-| `opencode.lines_of_code.total` | Gauge | Current cumulative lines added/removed for the session, refreshed on every `session.diff`. Drops back to `0` if opencode reports a revert to baseline. |
+| `opencode.lines_of_code.count` | Counter | Emits only the positive delta since the previous `session.diff`, so summing the counter avoids the old double-counting. **Caveats:** when opencode reports a cumulative drop (a revert), the negative delta is skipped — so summing the counter reflects gross additions across non-revert deltas and can overstate net after a revert. Rewrites that happen and are reverted *within a single message* aren't captured at all (opencode publishes the per-message cumulative, not intra-message churn). Use `opencode.lines_of_code.total` for the authoritative live total. |
+| `opencode.lines_of_code.total` | Gauge | Current cumulative lines added/removed for the session, refreshed on every `session.diff`. Drops back to `0` if opencode reports a revert to baseline. Authoritative for "what does this session currently amount to". |
 | `opencode.commit.count` | Counter | Git commits detected via bash tool |
 | `opencode.tool.duration` | Histogram | Tool execution time in milliseconds |
 | `opencode.cache.count` | Counter | Cache activity per message: `type=cacheRead` or `type=cacheCreation` |

src/handlers/activity.ts

@@ -1,6 +1,6 @@
 import { SeverityNumber } from "@opentelemetry/api-logs"
 import type { EventSessionDiff, EventCommandExecuted } from "@opencode-ai/sdk"
-import { isMetricEnabled } from "../util.ts"
+import { isMetricEnabled, setBoundedMap } from "../util.ts"
 import type { HandlerContext } from "../types.ts"
 
 /**
@@ -25,7 +25,7 @@ export function handleSessionDiff(e: EventSessionDiff, ctx: HandlerContext) {
   const prev = ctx.sessionDiffTotals.get(sessionID) ?? { additions: 0, deletions: 0 }
   const deltaAdded = totalAdded - prev.additions
   const deltaRemoved = totalRemoved - prev.deletions
-  ctx.sessionDiffTotals.set(sessionID, { additions: totalAdded, deletions: totalRemoved })
+  setBoundedMap(ctx.sessionDiffTotals, sessionID, { additions: totalAdded, deletions: totalRemoved })
 
   const baseAttrs = { ...ctx.commonAttrs, "session.id": sessionID }
 

src/handlers/session.ts

@@ -145,6 +145,7 @@ export function handleSessionError(e: EventSessionError, ctx: HandlerContext) {
   const rawID = e.properties.sessionID
   const sessionID = rawID ?? "unknown"
   const error = errorSummary(e.properties.error)
+  const totals = rawID ? ctx.sessionTotals.get(rawID) : undefined
   if (rawID) {
     ctx.sessionTotals.delete(rawID)
     ctx.sessionDiffTotals.delete(rawID)
@@ -154,7 +155,6 @@ export function handleSessionError(e: EventSessionError, ctx: HandlerContext) {
   if (rawID) {
     const sessionSpan = ctx.sessionSpans.get(rawID)
     if (sessionSpan) {
-      const totals = ctx.sessionTotals.get(rawID)
       if (totals) sessionSpan.setAttribute(AGENT_NAME, totals.agent)
       sessionSpan.setStatus({ code: SpanStatusCode.ERROR, message: error })
       sessionSpan.setAttribute("error", error)

src/otel.ts

@@ -147,11 +147,11 @@ export function createInstruments(prefix: string): Instruments {
     }),
     linesCounter: meter.createCounter(`${prefix}lines_of_code.count`, {
       unit: "{line}",
-      description: "Per-event delta of lines added/removed — sum over a session yields the net cumulative total.",
+      description: "Positive per-event delta of lines added/removed; sum reflects gross additions across non-revert deltas and may overstate net after a revert. Use lines_of_code.total for the authoritative live cumulative value.",
     }),
     linesTotalGauge: meter.createGauge(`${prefix}lines_of_code.total`, {
       unit: "{line}",
-      description: "Cumulative lines added/removed in the current session, refreshed on every session.diff.",
+      description: "Authoritative live cumulative lines added/removed for the current session, refreshed on every session.diff; drops back to 0 if opencode reports a revert to baseline.",
     }),
     commitCounter: meter.createCounter(`${prefix}commit.count`, {
       unit: "{commit}",