refactor(backend): extract shared session helpers — Kilo + OpenCode

[claudiusthebot]

Summary

Follow-up to #172. The previous PR unified MCP / sessions-lifecycle /
delivery / SSE between the two remote-server backends. This one
extracts the remaining big duplication: their sessions.ts
modules.

kilo/sessions.ts (593 LOC) and opencode/sessions.ts (492 LOC) had
~95% byte-for-byte duplication. Both contained the same:

• extractPartsSummary (parts → text + tool count + synthetic flag)
• extractAssistantUsage (token / cost from info blob)
• summarizeXAssistantMessages (batch → usage totals)
• getXTurnSummary / getXSessionSnapshot (high-level wrappers)
• rejectPendingQuestions (auto-handle question.list)
• Internal helpers: summarizeQuestionHeaders, isToolApprovalQuestion,
  parseAssistantMessage, listSessionMessages, etc.

The only meaningful difference was that Kilo's extractPartsSummary
peeled synthetic: true parts into a separate syntheticErrorText
channel; OpenCode's didn't.

What changed

New backend/remote-server/session-helpers.ts (541 LOC, mostly
docstrings) containing:

• RemoteAssistantInfo, RemoteSessionSnapshot, ParsedAssistantMessage, RemoteUsageSummary — shapes shared across backends.
• RemoteSessionClient — extends RemoteAgentClient with the session.messages + question.{list,reply,reject} methods these helpers need. Both KiloClient and OpencodeClient structurally satisfy it.
• REMOTE_SESSION_MESSAGE_LIMIT (5000).
• extractPartsSummary — now with synthetic-error detection. Both backends gain it.
• extractAssistantUsage
• summarizeAssistantMessages
• listSessionMessages
• getTurnSummary
• getSessionSnapshot (takes client as parameter so the shared helper doesn't bake in either backend's ensureServer)
• rejectPendingQuestions — with injected backendLabel for log prefixes (Auto-approved Kilo tool question vs Auto-approved OpenCode tool question).

kilo/sessions.ts and opencode/sessions.ts reduced to thin shims:

• Re-export shared helpers under backend-prefixed names for back-compat (KiloAssistantInfo / OpenCodeAssistantInfo are type aliases, getKiloTurnSummary / getOpenCodeTurnSummary wrap the shared getTurnSummary with backend-typed clients).
• getKiloSessionSnapshot / getOpenCodeSessionSnapshot thread their respective ensureServer() into the shared getSessionSnapshot.
• rejectPendingQuestions injects the backend label.

Behavioural change

OpenCode now ALSO recognises synthetic: true markers. Previously
documented as an asymmetry in the conformance test — synthetic is the
upstream's convention (Kilo + OpenCode emit it identically), so
symmetric handling is the right default. The conformance test for this
case has been updated to assert symmetric behaviour.

Dead-code removal

waitForPromptWithQuestionGuard and waitForAssistantReply deleted
from both backends. They were sync-prompt wrappers from the pre-SSE
era; both backends now use promptAsync + SSE (PR #172). Also dropped
from kilo/index.ts barrel re-exports.

Stats

File	Before	After	Delta
kilo/sessions.ts	593	100	−493
opencode/sessions.ts	492	102	−390
remote-server/session-helpers.ts (new)	—	541	+541
remote-server-session-helpers.test.ts (new)	—	396	+396

Net: 883 LOC of duplicated logic collapsed into one tested module +
thin shims.

Tests

• 24 new unit tests in remote-server-session-helpers.test.ts covering:
  • extractPartsSummary text joining, synthetic detection, reasoning filtering, edge cases
  • extractAssistantUsage zero defaults + full extraction
  • summarizeAssistantMessages aggregation, minCreatedAt filter, non-assistant skip, meaningful-message filter
  • listSessionMessages dedup, default limit, override limit
  • getTurnSummary end-to-end
  • getSessionSnapshot undefined-id, full snapshot construction, no-assistant case
  • rejectPendingQuestions tool-approval auto-allow, non-tool rejection, cross-session filter, idempotency, upstream-failure tolerance
• Updated synthetic-error case in backend-conformance.test.ts to assert symmetric behaviour
• Full suite: 2285 passing (+24 new), 12 skipped (live-tier), 0 failing

Test plan

• npx tsc --noEmit clean
• npm test — 2285 passing, 12 skipped, 0 failing
• npm run lint — 0 errors, 15 pre-existing warnings unchanged
• npm run format:check clean
• CI matrix on push
• Verify getKiloSessionSnapshot / getOpenCodeSessionSnapshot still return the right shape for /status (covered by existing kilo-summary tests via the shared summarizeAssistantMessages)

🤖 Generated with Claude Code