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code-session — driving a coding harness as data, not code ​

code-session is the stateful op-tool a Neo agent uses to OPERATE a coding harness — Claude Code, OpenAI Codex, GitHub Copilot, OpenCode, Factory Droid, or an internal Neo sub-agent (backend: 'neo', no external process) — live in a real repository: list the available harnesses and their track records, open a session from a brief, watch each turn (with a per-turn diff), send corrective guidance, answer mid-turn permission questions, escalate posture, and shut it down with an honest verdict. It is the substrate of the dev meta-harness initiative (Waves H0–H4, plan plans/stateless-cuddling-feather.md), built on the unified-agent foundation from Wave G (plans/wave-g-code-session.md, plans/agent-model.md §4.9/§5).

This is the ONLY dispatch path. There is no hand-written "Smith" controller left (retired Wave G chip G8) and no standalone code-specialist tool (retired Wave H1-B). A specialist is a .md persona granting code-session; the tool plus the persona ARE the mechanism. The source tree lives under src/tools/code-harness/ (renamed from code-specialist/ in Wave H0); the persona id, template filename (templates/agents/code-specialist.md), and the frozen code_specialist_* metric names stay for continuity.

1. The op contract ​

code-session is ONE buildTool-built tool (code-harness/code-session/tool.ts:1349 createCodeSessionTool), op-discriminated (deliberately not eight named tools — it keeps the dangerous surface at one registry name, excludable from channel auto-allow profiles). The op union and its I/O types are pure types in code-harness/code-session/contract.ts:201 (CodeSessionInput); the dispatch switch is tool.ts:1458.

opin (beyond op)out
startbrief, maxPosture?, initialPosture?, backend?, cwd?, agentModel?, effort?, maxRounds?, allowedTools?, appendSystemPrompt?, resumeSessionId?, taskTags?{ sessionId, backend, posture, maxPosture, maxRounds }
read-turnsessionId, includeDiff?one of the 5 closed kinds below, each with an optional turnDiff block
answersessionId, clarificationId, allow, reason?, note?{ ok:true, clarification }
guidesessionId, text, agentModel?, effort?{ ok:true }
set-posturesessionId, posture{ ok:true, posture }
interruptsessionId{ ok:true }
stopsessionId, outcome?, note?{ ok:true, alreadyStopped }
list-backends— (sessionless){ backends: HarnessBackendListing[] }

start ​

CodeSessionStartInput (contract.ts:35). Handled by handleStart (tool.ts:777): mints an unguessable sessionId FIRST (mintSessionId, 256-bit cs_…, contract.ts:352), opens the first turn's diff capture (§6), calls transport.start(...), then registers the live handle (registry.create, registry.ts:593). maxPosture is the CEILING for the session's whole lifetime (default 'acceptEdits', tool.ts:198); backend default is 'claude-code' (tool.ts:197). Parse/validate + scope-constraint enforcement is parseStartInput (tool.ts:432) — see §3 for the reject-explicit/clamp-default rules and §7 for the allowedTools/taskTags learning fields.

Terminal transport events can fire before registry.create runs for a coarse backend (neo, whose round boundary IS a whole runAgentLoop invocation); handleStart buffers pre-registration terminal events and flushes them in order after create (tool.ts:820-939).

read-turn — the closed result union (§4.9(iv)) ​

CodeSessionReadTurnInput (contract.ts:90), handled by handleReadTurn (tool.ts:981), which blocks on registry.awaitNextEvent (registry.ts:952) and maps the notification onto EXACTLY ONE of five kinds (CodeSessionReadTurnResult, contract.ts:284) — a tested switch, not emergent LLM behavior:

  • turn_complete — { actions, text, roundHistory, numTurns?, costUsd?, turnDiff? }. roundHistory is the PRE-TRUNCATED, compaction-immune diet (registry.getDiet → event-buffer.ts truncateDiet) so a compacted persona transcript never re-asks an answered clarification (§4.9(iii)).
  • clarification — { clarificationId, toolName, input }. Returns EARLY, mid-turn, while the driven agent's gated tool call is still blocked inside the transport's onClarify (§4.9(i)).
  • ended — { ok, text, turnDiff? }. The agent closed the session itself.
  • error — { message, turnDiff? }. Transport/agent failure.
  • max_rounds — { ok:true, text, rounds, turnDiff? }. Round cap hit; a CLEAN stop, not a failure.

includeDiff (contract.ts:99, read defensively at tool.ts:1023): every terminal (non-clarification) result carries a turnDiff block WHEN a diff was captured. The changed-file list + a one-line summaryLine are ALWAYS present (ReadTurnDiff, contract.ts:106; rendered by renderTurnDiffForReadTurn, tool.ts:741); the full unifiedDiff string is opt-in via includeDiff:true, to keep the driving persona's context lean.

answer / guide / set-posture / interrupt ​

  • answer (contract.ts:122, handleAnswer tool.ts:1083): resolves the pending clarification by id via registry.resolveClarification (registry.ts:825); a deny carries reason forward as next-turn guidance, and the outcome is pinned into the round history so truncateDiet can never drop it.
  • guide (contract.ts:136, handleGuide tool.ts:1118): pushes a next-turn instruction to session.sendGuidance; the driver steer is emitted/persisted as a guidance{source:'driver'} event (registry.recordDriverGuidance, registry.ts:901) but does NOT touch the round-history diet (the diet tracks the CHILD's actions). Optionally carries the Wave-J per-turn agentModel/effort switch (applied to the NEXT turn via CodeAgentSession.setModel) — accepted only for a modelSelection:'per-turn' backend (claude-code, codex), rejected loudly otherwise; see §10.
  • set-posture (contract.ts:148, handleSetPosture tool.ts:1143): a request above the ceiling is REJECTED, not clamped (§3).
  • interrupt (contract.ts:155, handleInterrupt tool.ts:1214): whole-turn abort via session.interrupt.

stop — with an optional verdict ​

CodeSessionStopInput (contract.ts:175), handled by handleStop (tool.ts:1252). Idempotent (alreadyStopped distinguishes "ours, already released" from a foreign/unknown id, which is a typed error). The optional { outcome, note } (chip H3-D) is the driver's authoritative VERDICT for the learning record: outcome ∈ 'success' | 'partial' | 'failed' | 'aborted' (CodeSessionStopOutcome, contract.ts:172, string-identical to HarnessOutcome). It is parsed loudly (optionalStopOutcome, tool.ts:368) and stashed on an in-process side channel (recordDriverStopSignal, harness-outcomes.ts:302) that the settle hook reads-and-clears (§7).

list-backends — capability matrix + track record ​

CodeSessionListBackendsInput (contract.ts:196), handled by handleListBackends (tool.ts:1310). Sessionless; the persona calls it FIRST to match harness↔task. For every registered transport it returns a HarnessBackendListing (contract.ts:319):

  • descriptor — the flattened capability descriptor (renderCapabilityDescriptor, capabilities.ts:379): strengths/weaknesses, posture map, live-control, resume, cost, briefingNotes, editToolNames.
  • availability — a LIVE probe (transport.probeAvailability, transport.ts:115); a throwing probe degrades to probe-failed rather than failing the op.
  • trackRecord? — short human lines distilled from past outcomes (buildHarnessTrackRecordLines, harness-outcomes.ts:248, TTL-cached ~60s); omitted when the backend has no history (§7). Since Wave J these include per-(backend, model) sub-lines for each model with ≥2 recorded runs, so the persona sees per-model win rates next to the routing guidance.
  • routingGuidance? — model/effort routing lines (Wave J, buildRoutingGuidanceLines, routing-catalog.ts): the backend's effort support + mechanism, its cost-profile framing (subscription = speed/rate-limit play; metered = dollar play), and how each agentModel class sentinel resolves. Sibling of trackRecord — advisory text, not data the tool interprets. See §10.

Backends registered in production ​

DEFAULT_TRANSPORTS (tool.ts:202) is { 'claude-code', codex }; the runtime merges additionalTransports additively (tool.ts:1352). tools-builtin.ts registers all six: claude-code (claude-code-sdk.ts), codex (codex-cli.ts), neo (internal-transport.ts), opencode (opencode-cli.ts), copilot (copilot-cli.ts), droid (droid-cli.ts). Per-backend capabilities, posture maps, install/auth, and quirks live in docs/harnesses.md. Tests full-override the map via CodeSessionToolDeps.transports (a fake transport, no subprocess).

2. The driver persona flow (a driver is data) ​

A driver persona is a .md agent definition (runtime/agent-definitions.ts) whose allowedTools is just code-session, whose model is the flagship class sentinel (resolved fresh at dispatch via resolveModelClass), and whose frontmatter sets driver: true plus the three policy knobs it passes to its own start calls (maxPosture, initialPosture, maxRounds). The shipped instance is templates/agents/code-specialist.md. The persona IS the brain — there is no separate "brain" LLM call; the persona's own agent-loop reasoning, expressed as code-session op calls, reproduces the retired Smith controller's judgment cadence.

The template's own flow (rewritten in chip H3-E):

  1. list-backends first — read every backend's capabilities + availability + track record, and pick the harness whose fit is best (never one whose probe is available:false).
  2. Capability matching — a task needing mid-turn gating wants clarifySupport:true; a fine-visibility task wants granularity:'stream'; a task that must stay inside Neo's own tool/memory wants neo.
  3. briefingNotes adaptation — each listing carries a "how to prompt THIS harness" string; the turn-1 brief is shaped accordingly (e.g. never pass allowedTools to a honorsAllowedTools:false backend — it is rejected loudly).
  4. taskTags — a few short tags describing the KIND of work, threaded into the outcome record for per-tag learning.
  5. Honest stop verdict — outcome marked success only when the brief was met AND verified by the agent's actions; a truthful verdict is what keeps future selection and hints correct.

Dispatch ​

Both production call sites route through dispatchCodeSpecialistPersona (persona-dispatch.ts:444), which runs the persona as an ordinary background delegation (runDelegatedAgentLoop, runInBackground: true) — the same machinery delegate({ agent, run_in_background }) uses. The two callers:

  • delegate({ supervised: true }) (tools/delegate.ts) — the single standalone entry. It pins the driven backend to neo via scopeConstraintOverrides: { backend: 'neo', allowedTools? }, restoring Smith's pre-Wave-G meaning (supervise an in-house Neo sub-agent).
  • any driver-persona delegate({ agent: '<name>' }) — a persona whose frontmatter pins a backend drives that external CLI/SDK instead.

Four things are specific to a driver (persona-dispatch.ts):

  • Duration exemption. maxDurationMs: 0 for a driver: true definition (persona-dispatch.ts:476) — the existing delegation.ts "non-positive ⇒ no timeout" seam, no new code.
  • Constraints in. Before boot, the persona's frontmatter policy (maxPosture/maxRounds/backend, constraintsFromDefinitionpersona-dispatch.ts:367), merged narrow-only with the caller's scopeConstraintOverrides (mergeScopeConstraintOverridespersona-dispatch.ts:405), is registered as ScopeConstraints (registry.setScopeConstraints, registry.ts:1066) keyed on the persona's ownership scope. op:'start' enforces them (§3) — a prompt-injected persona cannot pick its own ceiling.
  • Sweep out. On delegation settle (resolve OR reject), registry.releaseAllOwnedBy(scope) (registry.ts:1041) releases every session the persona opened and clears the scope's constraints. No subprocess outlives the persona; the dispatch layer never learns individual session ids.
  • Default definition loading. loadCodeSpecialistPersonaDefinition (persona-dispatch.ts:217) prefers an owner-installed ~/.neo/agents/code-specialist.md, and falls back to parsing the PACKAGED template read-only, so a fresh install dispatches correctly with no manual step. The template is excluded from the auto-installed starter roster because it is privileged (driver: true).

Also folded into the dispatcher: the outbox notifier (wireSettleNotifier/wireQuestionNotifier, the latter a PUSH subscription on BackgroundDelegationRegistry.onQuestion, persona-dispatch.ts:586/652), the frozen code_specialist_* metrics (wireMetrics, persona-dispatch.ts:614), the low-trust lesson block (§7, persona-dispatch.ts:506), and the outcome recorder (§7, wireOutcomeRecorder, persona-dispatch.ts:699).

3. Posture model ​

Neo's four postures order plan < default < acceptEdits < full (POSTURE_ORDER, code-session/posture.ts). Each backend maps them to its own permission representation via its descriptor's postureMap (capabilities.ts:139) — typed extractors (sdkPermissionModeForPosturecapabilities.ts:161, codexSandboxForPosture, neoPermissionModeForPosture, and the generic cli-flags target) replaced three hand-written switches. The per-backend mapping table is in docs/harnesses.md.

Two ceilings, both enforced at the tool layer, both loud on violation:

  1. Per-session ceiling. start's maxPosture is fixed for the session's whole lifetime. A later set-posture above it is REJECTED, not clamped (handleSetPosture, tool.ts:1162, plus the registry's belt-and-suspenders PostureCeilingExceededError, registry.ts:270). Rejecting rather than clamping stops an injected persona probing the ceiling silently by trial.
  2. Per-scope (persona) ceiling. ScopeConstraints (registry.ts:427) registered from the persona's frontmatter. In parseStartInput (tool.ts:432):
    • maxPosture — an EXPLICIT request above the ceiling is rejected (tool.ts:472, warned via code_session_start_rejected); an OMITTED default is silently clamped down (clampPosture).
    • backend — an explicit mismatch with a pinned backend is rejected (tool.ts:448); an omitted one resolves to the pin.
    • maxRounds — clamped (min) toward the constraint, never rejected (a resource budget, not a privilege surface; surfaces honestly as an earlier max_rounds).
    • allowedTools — omitted uses the constraint list outright; explicit is INTERSECTED (never widened); an empty intersection is rejected (tool.ts:542). Additionally, an explicit allowedTools aimed at a honorsAllowedTools:false backend is rejected loudly rather than silently ignored (tool.ts:527).

A scope with no registered constraints (the owner driving code-session directly) is unaffected. The ownership scope is the caller's agent-loop sessionId (deriveCodeSessionOwnership, tool.ts:317); one driver dispatch per session scope at a time is the supported shape.

4. The durable store (~/.neo/code-sessions/) ​

Chip H1-D. CodeSessionStore (code-session/session-store.ts) is a write-through MIRROR — the in-memory CodeSessionRegistry stays the source of truth the persona reads; the store makes visibility, restart-survival, and the learning substrate possible. Copied from src/memory/session-store.ts's patterns: per-session dir, atomic meta.json, per-session-serialized events.jsonl appends, graceful-null reads, failure-soft writes. Production callers share one lazy singleton (getCodeSessionStore, session-store.ts:461), wired into the registry at boot (tools-builtin.ts codeSessionRegistry.setStore).

Layout: ~/.neo/code-sessions/{sessionId}/meta.json + events.jsonl.

  • meta.json — CodeSessionRecord (session-store.ts:83): sessionId, backendId, cwd, model?, maxPosture, taskBrief (truncated to 2 KB, TASK_BRIEF_MAX_CHARS session-store.ts:105), taskTags, status (running | idle | ended | failed | orphaned), createdAt, updatedAt, roundsElapsed, costUsd?, runs[], version: 1. Published on create (createRecord, session-store.ts:198); patched on every transition (patchMeta, session-store.ts:212, read-modify-write under a per-session in-process lock).
  • runs[] — the resume chain (CodeSessionRun, session-store.ts:73): each entry is { startedAt, externalSessionId?, ownerScopeId }. The first run is written at create; a control-plane resume appends a second via appendRun (session-store.ts:294) rather than minting a new record. externalSessionId is the BACKEND's own session id (the transport's resumeSessionId target), distinct from the Neo-minted sessionId; on resume it is backfilled onto the latest run by setLatestRunExternalSessionId (session-store.ts) once the adopted run learns it (see §5's adoption note).
  • events.jsonl — one PersistedSessionEvent per line (session-store.ts:128): { seq, at, event }. seq is monotonic per session, assigned by the registry, never the store (registry.ts emitAndPersist), so on-disk order and seq order always agree — a reconnecting consumer resumes from a cursor via readEvents({ afterSeq }) (session-store.ts:392). The event payload (PersistedSessionEventPayload, session-store.ts:120) is a normalized CodeAgentEvent OR one of the registry annotations (guidance{source}, posture{mode}, clarification{toolName,decision?}, turn_diff). lastEventSeq(sessionId) (session-store.ts) reads the highest persisted seq (0 when empty) — the store's contribution to gapless resume: adopt seeds the revived session's next seq at lastEventSeq + 1 so the durable log continues without a gap or repeat, even across a restart.

Orphan sweep. sweepOrphaned (session-store.ts:423) marks every record still running/idle as orphaned — those were owned by the previous process's in-memory registry, which died with it. Run ONCE at daemon boot (cli/commands/daemon.ts:174, best-effort — a sweep failure never blocks boot).

5. Event seam + control-plane surface ​

Registry live-event seam (chip H1-D) ​

registry.onSessionEvent(listener) (registry.ts:561) is the ONE seam the control-plane bridge subscribes to; the same payload the store persists. Every state change funnels through emitAndPersist (registry.ts:1252), which assigns seq, broadcasts to listeners (each in try/catch — a throwing listener is isolated), and — when a store is wired — persists. Emit is a no-op once released, so the release lifecycle event is guaranteed the LAST event a session produces. Raw fidelity (tool_use/text/tool_result) is forwarded via recordAgentEvent (registry.ts:690); captured diffs via recordTurnDiff (registry.ts:706); user steers via injectUserGuidance (registry.ts:859).

Bridge (chip H3-A) ​

createCodeSessionBridge (control-plane/code-session-bridge.ts:76) maps the seam onto two event-hub topics (registered in event-hub.ts's EventTopic and routes.ts's ALL_TOPICS, routes.ts:162):

  • code_session_event — one hub event per live registry event, payload = CodeSessionLiveEvent verbatim. Incremental text events are COALESCED per session on a 250 ms window (TEXT_COALESCE_MS, code-session-bridge.ts:44, last text wins) so a chatty narration can't flood SSE — full fidelity still lands in events.jsonl. Every other kind passes through immediately, flushing any pending coalesced text first to preserve seq order.
  • code_session_changed — a meta/status transition, payload = { record }. Fetched on a short per-session debounce (CHANGED_DEBOUNCE_MS, 250 ms, code-session-bridge.ts:47) so the registry's fire-and-forget meta.json write-through has landed before the read. Only STATUS_AFFECTING_KINDS (started/turn_complete/ended/error/guidance, code-session-bridge.ts:55) trigger a republish.

close() unsubscribes and clears every timer on shutdown. Composed into the daemon at cli/commands/daemon.ts:498, subscribing to the process-wide codeSessionRegistry singleton.

Routes (chip H3-A) ​

createCodeSessionRoutes (control-plane/routes.ts:940) — four bearer-gated /api/* routes over the {ok,data}|{ok:false,error} envelope, mounted in the daemon at cli/commands/daemon.ts:623:

  • GET /api/code-sessions → { sessions: CodeSessionRecord[] } (store.list(), newest first).
  • GET /api/code-sessions/:id?afterSeq=N&limit=M → { record, events } (store.get + store.readEvents); 404 when missing. afterSeq is the SSE resume cursor.
  • POST /api/code-sessions/:id/guidance {text} → injects USER guidance (registry.injectUserGuidance, pinned into the persona's round history so it SEES it) then delivers via session.sendGuidance. 400 empty text, 404 unknown, 409 (CodeSessionNotLiveError, registry.ts:256) when the record exists but is no longer live (must be resumed first).
  • POST /api/code-sessions/:id/resume → dispatch a fresh supervised delegation resuming an ended/failed/orphaned record, appending its run to the SAME record's runs[]. 404 missing, 409 when still live, 503 only if no resume dispatcher is wired (not the case in the daemon).

Resume wiring (chip H4-A). The daemon supplies the route's resumeDispatch via createDaemonResumeDispatcher (code-session-resume.ts:152), built next to the code-session bridge (daemon.ts:525) and passed into createCodeSessionRoutes (daemon.ts:657). It reuses dispatchCodeSpecialistPersona — no parallel dispatch path: the resume brief carries the record's taskBrief/cwd/maxPosture ceiling and (when captured) the last run's externalSessionId as resumeSessionId, and pins the backend via scope-constraint override. Because the daemon builds no AgentDependencies of its own, the dispatcher lazily builds ONE embedded runtime on first resume and borrows its deps bag (EmbeddedNeo.getAgentDependencies(), types.ts:164) — which wires the same module-level registry the bridge watches, so resumed sessions surface on the live feed. Each resume gets its own synthetic ownership scope (code-resume- prefix) so one resume's settle-sweep can't tear down another's live session. A failed dispatch → 500 with the real reason and the record's runs[]/status untouched.

Record adoption (chip H4-D). The resumed persona's op:'start' no longer mints a fresh Neo-side record — it ADOPTS the original, so a resumed task stays on ONE record (the dashboard shows one, not two). The dispatcher pins scopeConstraintOverrides.adoptRecordId = record.sessionId alongside the backend pin; that flows into registry.setScopeConstraints(scope, { …, adoptRecordId }), and the code-session tool's op:'start' (tool.ts handleStart), seeing the pin, calls registry.adopt(recordId) instead of mintSessionId + create for the FIRST start in the resumed persona's scope. adopt (registry.ts):

  • revives the record under its own id (preserving taskBrief/createdAt/ taskTags/runs[]; hard-errors CodeSessionAlreadyLiveError if it is still live in-registry, CodeSessionAdoptRecordNotFoundError if no record/store),
  • continues the durable events.jsonl GAPLESSLY (nextSeq = lastEventSeq + 1, including across a restart) and continues the round budget from roundsElapsed,
  • backfills the backend session id onto the latest run (the one the route appended), and
  • is ONE-SHOT: the tool clears the pin (clearAdoptConstraint) right after, so a later start in the same scope mints fresh (the persona may legitimately open additional sessions).

Division of labour: the ROUTE owns the appendRun + patchMeta({running}) (synchronous, before the persona's async first turn); adopt never appends a run, so exactly one is added per resume. E2E + adopt-unit coverage: tests/integration/code-session-resume.test.ts, tests/tools/code-session-adopt.test.ts, tests/tools/code-session-tool.test.ts.

Web (chip H3-B) ​

apps/web/src/components/code-sessions/** renders the list (status/backend/ model/cost/rounds) and a detail view with a live SSE feed, tool-call cards, a posture badge, and DiffView (the codebase's first unified-diff renderer), a guidance input (POST), and a resume button. Delegations rows link to the driving session.

Terminal attach — resuming a session from your own shell ​

Neo's own POST /api/code-sessions/:id/resume above kicks a fresh SUPERVISED run (a driving persona resumes control). Separately, an owner sometimes wants to attach directly, from their own terminal, to the backend CLI/SDK session Neo drove — e.g. to poke at it by hand after Neo's run ended or orphaned. That affordance is descriptor-driven, not hardcoded:

  • HarnessCapabilityDescriptor.externalAttach (tools/code-harness/ capabilities.ts for the H1 backends, or next to each backend's own transport per the Wave-H2 convention) is an OPTIONAL { commandTemplate, note? } per backend — the backend's own evidence-verified INTERACTIVE resume command (distinct from resume, which describes how the TRANSPORT resumes a session programmatically). Backends with a live-cited interactive resume command: claude-code (claude --resume {sessionId}, claude-code-src/src/main.tsx:988's -r, --resume [value]), codex (codex resume {sessionId}, codex-src/codex-rs/cli/src/main.rs:2642's own exit-hint text), and opencode (opencode "{cwd}" --session {sessionId}, a live opencode --help capture 2026-07-12 — the {cwd} project positional is safety-critical, not decorative: opencode resolves its project root from its own persisted state rather than the launching process's cwd, so a rendered command with an empty cwd is refused outright rather than risk attaching to the wrong repo). neo omits it outright — its "sessions" are in-process agent-loop rounds with no external CLI to attach to. copilot/droid have no confirmed interactive-resume evidence yet, so they carry no field — loud omission, never a guessed flag (see scratch/attach-affordance-notes.md's evidence table).
  • GET /api/code-sessions/:id (control-plane/routes.ts) computes an optional externalAttach: { command, note? } on the response — the descriptor's template filled in with the record's LATEST run externalSessionId and cwd — via renderExternalAttachCommand. Absent when the backend has no externalAttach descriptor, no run ever captured an externalSessionId, or cwd was never recorded and the backend's command needs it as a real argument (opencode). The client renders the finished string only; no template logic ships to the browser.
  • CodeSessionDetail shows the command in a monospace row with a Copy button when present. If the session is still running/idle, it also shows a caution line: attaching from a terminal while Neo is still driving means two drivers on one session — resume from the terminal only after the session ends.

6. Diff capture (chip H3-C) ​

diff-capture.ts produces a TurnDiffSummary (diff-capture.ts:72) per turn — a bounded file list (A/M/D/R + insertion/deletion counts) and, on request, a capped unified diff. Hybrid, best-effort, never throws (a capture problem must never break the read-turn that triggered it):

  1. git (source:'git', computeGitDiff diff-capture.ts:249) — the primary path when cwd is a git work tree. At turn START, snapshot HEAD + status --porcelain -z -uall (snapshotStart, diff-capture.ts:228); at turn END, diff -M <startHead> (folds in mid-turn commits) plus newly-untracked files (rendered via diff --no-index). Rename detection on (-M).
  2. tool-events (source:'tool-events', fallbackSummarydiff-capture.ts:316) — the fallback when git is unavailable: paths accumulated from tool_use events whose tool name is in the backend descriptor's editToolNames (extractEditPaths, diff-capture.ts:333), each a { path, status:'M' } with no line counts.

Neither yielding ⇒ source:'none', files:[]. All git runs go through execFileNoThrow (execa, never a shell) with -z NUL-delimited output, so Windows paths with spaces/backslashes/non-ASCII are argv-safe. The unified diff is capped to 64 KB (DEFAULT_MAX_DIFF_BYTES, diff-capture.ts:134; truncated:true + a marker line when exceeded).

Wired around turn boundaries in tool.ts: the session's capture is created and its turn-1 baseline snapshotted BEFORE transport.start() (tool.ts:797-806, so a coarse in-process neo backend can't race the snapshot); each terminal read-turn calls settleTurnDiff (tool.ts:685) to finish the current turn's diff, persist it via registry.recordTurnDiff, cache it, and open the next turn's baseline. The persisted turn_diff event (pre-capped) rides events.jsonl and the live feed so the DiffView renders without touching the persona's registry.

7. The learning loop (data, not code) ​

Fully automatic — no human review gate. Safety comes from the low-trust injection wrapper + an evidenceCount ≥ 2 gate + confidence decay/eviction; lessons never become executables and never influence posture ceilings.

Outcomes (~/.neo/learning/harness-outcomes.jsonl, chip H3-D) ​

observability/harness-outcomes.ts. On delegation settle, wireOutcomeRecorder (persona-dispatch.ts:699) appends one HarnessOutcomeRecord (harness-outcomes.ts:93) per code session the persona drove. Because the settle sweep has already released those sessions from the in-memory registry, the durable store is the source of truth for "which sessions did this scope own" (matched on runs[].ownerScopeId, persona-dispatch.ts:727). Idempotent per session (claimOutcomeRecording, harness-outcomes.ts:323).

The record carries backendId, model?, effort?, taskTags, rounds, durationMs, costUsd?, outcome, interventions, failureReason?, driverNote?. model/effort (Wave J §5) make routing self-improving: the resolved CONCRETE model id is always recorded — pinned via agentModel, or, for a backend-default run, captured from the transport's started event (F5, so default runs are no longer unattributed) — and effort records the level the session ran at, threaded op:'start' → registry.create → CodeSessionRecord → the settle hook. This lets the distiller separate "haiku@low failed" from "haiku@high failed" and lets list-backends render per-model win rates. The outcome is the driver's explicit stop verdict when given (takeDriverStopSignal), else INFERRED (deriveHarnessOutcome, harness-outcomes.ts:462; inference never yields partial — that is driver-only). interventions (countInterventions, harness-outcomes.ts:372) counts user-guidance events, clarifications (at raise), posture escalations, and interrupts from the persisted events; sumSessionCost (harness-outcomes.ts:411) folds costUsd across turn boundaries.

buildHarnessTrackRecordLines(backendId) (harness-outcomes.ts:248, TTL-cached ~60 s, invalidated on each new record) renders the list-backends track-record line, e.g. "codex: 7 runs, 71% success, avg 4.2 rounds, last failure: … (3d ago)".

Lessons (~/.neo/learning/harness-lessons.json, chip H3-E) ​

memory/distillation/harness-lesson-distiller.ts. A nightly pass (runHarnessLessonDistillationPass, harness-lesson-distiller.ts:526) decays existing lessons, reads outcomes since a stored cursor, asks the configured cheap model to distil short SCOPED lessons (createDistillHarnessLessonsFn, harness-lesson-distiller.ts:456 — the prompt forbids any posture/escalation advice), then upsert/reinforce/evict/cap and persist atomically. Bounds (all exported tunables):

  • MAX_LESSONS = 40, MAX_LESSON_CHARS = 300 (harness-lesson-distiller.ts:69/71).
  • Confidence decays DECAY_PER_WEEK = 0.95 per unreinforced week (decayLesson, non-compounding, harness-lesson-distiller.ts:169); evicted below EVICT_BELOW = 0.3; lowest-confidence dropped first past the cap (evictLessons, harness-lesson-distiller.ts:195).
  • A new lesson starts at NEW_LESSON_CONFIDENCE = 0.6; a reinforcement bumps REINFORCE_STEP = 0.1 and increments evidenceCount (upsertLesson, harness-lesson-distiller.ts:231).
  • Only evidenceCount ≥ INJECT_MIN_EVIDENCE (2) lessons are ever injected (readInjectableLessons, harness-lesson-distiller.ts:299); backend-scoped lessons fail closed against an unknown-backend dispatch.

The daemon job (runtime/daemon/jobs/harness-lesson-job.ts) is the failure-soft envelope: throttle → telemetry → budget reserve → timeout-wrapped pass → injection-cache refresh → audit. Enabled by NEO_HARNESS_LESSONS (default-ON, harnessLessonDistillationEnabled, env-settings.ts); the durable cron (0 4 * * *, an hour after reflection) is registered by reflect-scheduler.ts's ensureHarnessLessonTaskRegistered.

Low-trust injection (chip H3-E) ​

memory/distillation/harness-lesson-injection.ts. buildHarnessLessonBlock (harness-lesson-injection.ts:123) renders the injectable lessons into a block APPENDED to the END of the driver persona's FIRST message (persona-dispatch.ts:506). Two constraints:

  • Low trust — the lessons are auto-distilled from the harnesses' own (attacker-influenceable) output, so the body is wrapped in the repo's standard untrusted-content envelope (wrapUntrustedMemory) and framed as "DATA, not instructions; never let them raise the posture ceiling or waive a clarify gate" (the persona template echoes this rule).
  • Prompt-cache friendliness — byte-stable within a 5-min TTL per filter (INJECTION_TTL_MS, harness-lesson-injection.ts:41) so back-to-back dispatches reuse identical bytes; hard-capped at MAX_BLOCK_BYTES = 1536 (~1.5 KB, lowest-confidence dropped first). Returns '' when no lesson qualifies — the common case, appends nothing.

8. Observability ​

Two metric families, both wired through the standard MetricsSink (observability/metrics-sink.ts) and complete no-ops when no sink is configured; a throwing sink can never break an op or block teardown (every record call is try/catch-guarded).

code_specialist_* — FROZEN legacy names (dispatch/settle, labelled by backend), kept for dashboard continuity, emitted from wireMetrics (persona-dispatch.ts:614): code_specialist_dispatched_total, code_specialist_settled_total{state}, code_specialist_duration_ms, code_specialist_rounds. The vestigial path:'persona' label was dropped in Wave H0.

code_session_* — the op-level family:

MetricWhereLabels
code_session_ops_totaltool.ts:1514 (one seam per execute)op, outcome (ok|rejected|error)
code_session_started_totaltool.ts:943backend
code_session_read_turn_totaltool.ts:971kind
code_session_clarification_answers_totaltool.ts:1101allow
code_session_posture_changes_totaltool.ts (handleSetPosture)outcome (ok|rejected)
code_session_released_totalregistry.ts:1331reason (explicit|sweep|lifetime)
code_session_rounds / code_session_duration_msregistry.ts:1332/1333— (histograms, at release)
code_session_settled_totalpersona-dispatch.ts:801backend, outcome (learning)
code_session_settle_duration_mspersona-dispatch.ts:802backend

Decision logs (log.info/log.warn) mirror the retired Smith controller's per-round narration: code_session_created/_released/_scope_swept (registry.ts), code_session_read_turn, code_session_clarification_raised/ _answered, code_session_posture_set/_rejected, code_session_guide, code_session_interrupt, code_session_start_rejected (tool.ts).

The registry is a module-level singleton constructed at import time, before the process's MetricsSink/store exist — so both are wired via setters (setMetricsSink registry.ts:581, setStore registry.ts:546; idempotent, last call wins), called from tools-builtin.ts alongside createCodeSessionTool.

9. Capability curation (Wave I) ​

Before a driven code-session starts in a repo, Neo provisions exactly the capabilities THAT project needs — skills, MCP servers, instruction text — from official, pinned sources only, session-scoped (no repo pollution), with owner approval gating executable components. A Supabase project gets Supabase capabilities; a plain repo gets none of that noise. Four modules, one per chip, wired together by chip I4:

ChipModuleOwns
I1capability-catalog/{types,catalog,identity,ledger,refresh}.tsThe typed catalog (8 v1 entries), trust tiers, the approval ledger, refresh probing
I2project-profile.tsPer-project DETECTION (file-exists/package-dep/file-content/workflow-action/compose-service rules), cached
I3provisioning/{types,plan-builder}.tsPer-backend plan BUILDING (materializes session-scoped MCP config/skills/instructions)
I4code-session/{capability-provisioning,capability-skill-fetcher}.tsThe pipeline wiring + visibility (this section)

Pipeline: detect → gate → provision → visibility ​

resolveSessionProvision (code-session/capability-provisioning.ts) sequences the three layers for one op:'start' call:

  1. Detect — buildProjectProfile(cwd, catalog) (I2) evaluates every catalog entry's DetectionRule[] against the repo, cached under ~/.neo/project-profiles/. Skipped entirely when cwd is omitted — capability curation is explicitly per-PROJECT; defaulting to process.cwd() would mean scanning wherever the Neo process happens to be running FROM (the daemon's own install dir, or — in the test suite — the Neo repo checkout itself), not the project being worked on.
  2. Gate on trust — for each detected capability, CapabilityTrustLedger .assertUsable(entry) (I1, capability-catalog/ledger.ts) passes T0/T1/T2R through with NO gate; a T2/T3 entry not yet approved throws CapabilityApprovalRequiredError. That capability is DEFERRED (excluded from this session's plan) and requestCapabilityApproval(entry, { queue }) files an owner-approval request through the EXISTING workflows/ApprovalQueue — never a parallel notification channel. The session is NEVER blocked waiting on an approval; a future session in the same project picks the capability up automatically once approved (approval binds to the entry's pinned identity, so a later pin bump re-prompts).
  3. Provision — buildProvisionPlan({ backendId, capabilities, sessionDir, fetchSkill }) (I3, provisioning/plan-builder.ts) materializes the backend-tailored ProvisionPlan under <sessionDir>/provision/ (MCP config, skill dirs, an instructions file — never in the target repo) and rides in on StartSessionOptions.provision. sessionDir is registry.getStore()!.getSessionDir(sessionId) — the SAME store the registry's write-through uses (never the process-wide singleton directly, so an isolated test registry+store pair never has provisioning reach outside its own sandbox). fetchSkill is the real, network-backed createGithubSkillFetcher (code-session/capability-skill-fetcher.ts, chip I4) — a recursive GitHub Contents API walk pinned to the catalog entry's exact commitSha, never HEAD/a branch.
  4. Visibility — the outcome is persisted onto the session record as CodeSessionRecord.provision (CodeSessionProvisionMeta, session-store.ts): capabilityIds (everything DETECTED, not just provisioned), applied/ignored (mirroring the transport's own provision event), tiers (capability id → trust tier), awaitingApproval (deferred T2/T3 ids — so the owner sees "playwright: awaiting approval" on the record even though nothing was provisioned this session), and tokenScopeNotes (see below). Written via store.patchMeta right after registry.create/adopt, serialized onto the SAME per-session withInProcessLock queue those calls' own write acquired first — see tool.ts handleStart's comment for why this ordering is guaranteed regardless of promise-settle timing. No route change was needed for this to reach GET /api/code-sessions/:id — §5's routes already serialize record verbatim.

Call site: tool.ts handleStart, right before transport.start() — NOT persona-dispatch.ts. The driving persona's cwd is free-form prose folded into its task text (tools/delegate.ts's buildSupervisedDirectives), not a structural field available before the persona itself calls op:'start'; parsed.cwd/parsed.backendId in handleStart are the only place a concrete, final value exists.

Owner guidance: T2R remote MCP has no URL-level read-only param ​

Some vendor-hosted (T2R) MCP servers — GitHub, Stripe — expose no URL query parameter that forces read-only access (unlike Supabase's read_only=true scope param). Safety for those rests ENTIRELY on the scope of the token bound to the capability's authEnv (a read-only GitHub PAT, a Stripe RESTRICTED test-mode key — never a live secret). Neo cannot enforce this. Chip I4 surfaces the caveat on the VISIBILITY layer: every applied capability whose MCP spec carries an authEnv gets a tokenScopeNotes entry (capability-provisioning.ts's tokenScopeNoteFor), rendered alongside the record's other capability meta. (I1's capability-catalog/ledger.ts already carries an equivalent caveat in the T2/T3 approval PROMPT text itself, via requestCapabilityApproval's pinSummary/question builder — that file is I1's exclusive surface, so I4 adds the caveat at the visibility layer rather than editing it.) If you approve a GitHub or Stripe capability, verify the bound token is scoped read-only / restricted-test-mode yourself — there is no technical control that enforces it.

Approval composition roots ​

bindApprovalResolutions(queue, ledger, catalog) (I1) must be wired to the SAME ApprovalQueue instance whatever surface actually calls .resolve() uses — ApprovalQueue.onResolved is an in-process EventEmitter, not a disk poll, so a resolution against a DIFFERENT queue instance never fires it (the same limitation every other ApprovalQueue consumer in this codebase already lives with — e.g. workflow step resumption). Two composition roots wire it, both unconditionally (a no-op for every non-capability:-prefixed approval):

  • Daemon: runtime/daemon/workflow-host.ts's createDaemonWorkflowHost, right after constructing its ApprovalQueue (alongside the existing wireApprovalNotifications opt-in wiring).
  • Embedded/interactive runtime: runtime/embedded/tools-workflow.ts's initWorkflowTools, right after constructing its ApprovalQueue.

Both also call codeSessionRegistry.setApprovalQueue(queue) — a setter (registry.ts, mirroring setStore/setMetricsSink) — so op:'start''s provisioning step can reach the queue to file a capability approval. No queue wired (a minimal/test composition) means a gated capability is simply withheld, never requested; the session is never blocked either way.

Refresh job (data only — never bumps a pin) ​

runtime/daemon/jobs/capability-refresh-job.ts runs checkForUpdates (loadCapabilityCatalog(), createHttpUpdateFetcher({ githubToken })) (I1, capability-catalog/refresh.ts) on a weekly cron (0 5 * * 0 default, NEO_CAPABILITY_REFRESH_CRON override; ensureCapabilityRefreshTaskRegistered, runtime/reflect-scheduler.ts), registered by scheduler-host.ts under the 'capability-refresh' system tag (NEO_CAPABILITY_REFRESH, default-ON — cheap network probes against GitHub/npm's public APIs, no LLM call, no human gate to enable it). When the report finds an available update it pushes ONE owner notice (mirroring approval-notifications.ts's channel-broadcast pattern) listing each pinned source's delta. Bumping a pin stays a human, reviewed catalog edit — this job produces data, never a write to catalog.ts.

Test coverage ​

  • tests/tools/code-session-capability-provisioning.test.ts — the detect→gate→provision→meta pipeline (no network; buildProfile/ledger/ fetchSkill are injected).
  • tests/tools/code-session-capability-skill-fetcher.test.ts — the GitHub Contents API walker (fetchImpl injected; no network).
  • tests/tools/code-session-tool.test.ts (describe: "capability curation") — end-to-end through the REAL catalog + detector against a fixture repo dir (a fake transport is still used, as everywhere else in that suite); NEO_HOME sandboxed to a temp dir for that block.
  • tests/runtime/daemon/jobs/capability-refresh-job.test.ts — the refresh job's envelope + owner-notice fan-out (fetcher injected; no network).
  • Cleanup guarantee (a provisioned session's materialized artifacts are always removed): already covered by the COMBINATION of tests/tools/code-harness-provisioning.test.ts (I3 — each transport's stop() calls cleanupProvisionArtifacts) and this file's own op:'stop' coverage (every release path funnels through registry.releaseEntry, which always calls session.stop() — registry.ts:1442); no new test was needed.

10. Model + effort routing (Wave J) ​

The persona picks the RIGHT model + reasoning effort per task — not always the strongest. The design is the Wave-I pattern exactly: deterministic DATA + persona discretion, no router service, no new preference table. Knowledge splits across the three channels the persona already reads.

The two knobs ​

  • agentModel (op:'start' and per-turn op:'guide') — a concrete backend model id, OR a model-CLASS sentinel 'cheap' | 'standard' | 'frontier' (ModelTier, providers/model-router.ts, reused verbatim — no new vocabulary). Resolved at parse time (resolveAgentModelForBackend, tool.ts) via the backend descriptor's modelClassMap (capabilities.ts); null/absent entries and backend:'neo' collapse to "omit the flag". The post-resolution CONCRETE id reaches the transport AND the persisted record (F5 — never the sentinel).
  • effort (same two ops) — low | medium | high | max (CodeSessionEffort, canonical in transport.ts, re-exported by contract.ts). Parsed + LOUD-rejected (parseEffortInput / assertEffortSupported, tool.ts) against the backend descriptor's effortSupport — 'none'/'unknown'/absent all reject, mirroring the honorsAllowedTools precedent. Threaded onto StartSessionOptions.effort and, for neo, into the provider-level extended-thinking config (first caller of that plumbing).

Where the knowledge lives ​

  1. Per-backend mechanics → the descriptors (capabilities.tseffortSupport/modelClassMap; each CLI transport for its own). Per-backend effort table + the UNKNOWN-until-J7 status is in docs/harnesses.md.
  2. Cross-cutting knowledge → code-session/routing-catalog.ts: TASK_CLASS_GUIDANCE (advisory (model class, effort) per task class per cost-profile), resolveAgentModelClass (sentinel → concrete id, delegating to resolveTier for neo — the ONE tier-policy home), and buildRoutingGuidanceLines (renders the list-backends routingGuidance).
  3. Judgment/discipline → the persona template's "Choosing model + effort" section (default = backend-default @ medium; downshift for bounded work; upshift effort only on retry-after-failure or hard briefs; never route agentic work at a model with unverified tool-calling; :free tiers only for public/low-sensitivity repos).

Per-turn switching ​

claude-code and codex descriptors are modelSelection:'per-turn' (J2 wired CodeAgentSession.setModel — query.setModel() for claude-code, mutable argv for codex). op:'guide' carrying agentModel/effort calls setModel for the NEXT turn (handleGuide, tool.ts); every other backend rejects the switch loudly. The effort half ships DORMANT behind J7 verification for both (their effortSupport stays 'unknown' until J7 confirms the SDK field name / CLI spelling — an explicit effort is loud-rejected until then), while the model switch is live now.

The feedback loop (self-improving, no new stores) ​

Outcomes are now model+effort-attributed (§7), so the nightly distiller produces model-scoped lessons ("qwen3-coder:free loses track on multi-file refactors") and list-backends renders per-(backend, model) win-rate sub-lines next to the routing guidance — the persona's selection loop closes on real evidence.