Phase A: harness/web pre-work foundation

[ytallo]

Summary

Multi-crate foundation that unblocks the harness/web Phase B refactor (#TBD). Adds bus surfaces, dual-write semantics, and a UI message reader/reducer that survive WS interleave.

What's in the box

session-tree — exposed surface

• session-tree::list {limit?, offset?, order?: "asc"|"desc"} → {sessions, total} with pagination + ordering. Default desc by updated_at. Backed by existing SessionStore::list().
• session-tree::messages response now [{entry_id, message}] (was AgentMessage[]). Breaking — only session-tree's own tests called it before.
• session-tree::ensure {session_id} — caller-supplied idempotent create.
• session-tree::reconcile {session_id, state_snapshot} → {state_count, tree_count_before, tree_count_after, repaired} for repairing state↔tree drift on demand.

turn-orchestrator — dual-write

• persistence.rs::save_messages writes to state::* (canonical) + best-effort session-tree::append for the delta. Lazy session-tree::ensure on first append; failures log warn and continue (never abort the turn).
• New state key last_session_tree_len_key tracks how many messages have been mirrored, so re-saves don't re-append.

harness

• approval-gate added to EXPECTED_WORKERS + iii.worker.yaml so approval_required from the UI actually blocks. Drift test enforces alignment.

harness/web

• loadMessagesWithEntryIds(sessionId) — UI helper that prefers session-tree::messages and falls back to state::get on empty/error. Drift case (no entry_ids) returns entry_id: null so callers can disable fork buttons with a tooltip.
• reducer.ts rewritten: entry-id-keyed Map, idempotent under any arrival order, patch-merge for streaming deltas, lastEntryId checkpoint for replay-after-reconnect, unknown event types ignored (forward-compat). Old per-message ad-hoc dedupe removed.
• visibleMessages(state) consumer helper composes the keyed + unkeyed view.

iii-browser-sdk (separate repo)

Companion PR: iii-hq/iii#1611 — adds addConnectionStateListener on ISdk so consumers can observe WS connection state. Already merged + published as iii-browser-sdk@0.11.7-next.1. Phase B consumes it.

Test plan

• cargo test --lib clean across harness (4), session-tree (42), turn-orchestrator (63)
• cargo test --tests clean — incl. new harness/tests/phase_a.rs E2E (dual-write → fork → simulated drift → reconcile)
• cargo clippy --lib --tests -- -D warnings clean across all changed crates
• harness/web vitest: 13 passing (reducer + loadMessages)
• tsc --noEmit clean
• npm run build clean
• Branch verified end-to-end against demo.sh stack (16 workers including approval-gate)

Risks & deferred items

• D-4 forced session-tree failure test deferred — needs a fault-injection harness. The structural guarantee (no ?/unwrap on session-tree calls in mirror_messages_to_session_tree) is enforced by code review.
• Cross-crate test binary lookup in tests/common/mod.rs walks ../session-tree/target/... with env override. Acceptable as v1; follow-up could use cargo metadata.
• App.tsx call-site migration to the new helper is intentionally Phase B work.

Commit history

12 atomic commits, TDD throughout. Each commit is independently buildable + testable.

6d7e11d test(harness): Phase A E2E acceptance — dual-write + fork + reconcile
069689a feat(harness/web): rewrite reducer to entry-id-keyed Map; idempotent + replay-safe
3132e19 feat(harness/web): add loadMessagesWithEntryIds helper with state::* fallback
2ceb673 feat(session-tree): add session-tree::reconcile to repair state↔tree drift
371761c test(turn-orchestrator): dual-write delta + lazy-create tests; abort mirror on parent-read failure
181a41d feat(turn-orchestrator): dual-write messages to session-tree (best-effort mirror)
6fc2c5a feat(session-tree): add session-tree::ensure for caller-supplied idempotent create
1bb5382 test(session-tree): serialize bus tests to avoid iii port collision
7d529c9 test(session-tree): bus-level integration tests for list + messages entry_ids
38f7086 feat(session-tree): add entry_id to session-tree::messages response (BREAKING)
387d7a8 feat(session-tree): add session-tree::list bus function with pagination + ordering
8883b1b feat(harness): add approval-gate to EXPECTED_WORKERS + iii.worker.yaml

[coderabbitai]

Important

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📥 Commits

Reviewing files that changed from the base of the PR and between 1cf885a and 4a84cc7.

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