# Implementation Decision Log — Orchestrator (Phase 2)

Han synthesis output. Each decision is committed: it cites evidence, records
rejected alternatives, names an owner, and a revisit criterion. Cross-reference
invariant: every `D-N` here is referenced by [design.md](../design.md) and/or
[tasks.md](../tasks.md), and produced by a round recorded in
[implementation-iteration-history.md](implementation-iteration-history.md).

Source: a conversational `grill-me` design session. The settled behavioral spec
is captured in [design-context.md](design-context.md) (12 decisions; decision 5
is REVISED by D-3 / D-4 below). Specialist findings are in the claim ledger
C1–C16 of the iteration history.

Trust class of evidence below: **codebase** (file:line in this repo) unless
noted. No single-source web claims underpin any committed decision.

---

## D-1 — Re-home the pure conductor definitions into `apps/coder/src/conductor/`

**Decision.** Copy the pure (dispatch-free) conductor definition files —
`spine.ts`, `flows/*`, `contracts.ts`, `types.ts`, `render.ts` — into
`apps/coder/src/conductor/`, plus the 23 Han personas (`conductor/agents/*.md`).
The Phase-1 standalone CLI (`conductor/`) stays alive and unchanged. Sever the
`flows/code-review.ts` → `dispatch.ts` coupling by adding a `DispatchFn` to
`StepContext`, injected by the flow-runner. Parameterize `spine.ts`'s model from
`process.env.CONDUCTOR_MODEL` to the run's configured model.

**Rationale.** The flow definitions are pure data + closures; only `dispatch.ts`
(the `opencode run` subprocess path) and `flow.ts` (the in-memory scheduler) are
Phase-1-specific. Copying the pure files avoids a workspace-package extraction
(YAGNI — only two consumers) while keeping the Phase-1 CLI as a regression
oracle. The evidence/yagni contracts are preserved because the flow-runner calls
`step.run(ctx)` in-process to build each prompt BEFORE inserting the task — the
closures execute in the coder process; prompts are never serialized to DB.

**Evidence.** `code-review.ts:10` (`import { dispatchAgent } from '../dispatch.js'`)
and `:62` (the per-dimension dispatch call) — the only flow→dispatch coupling
(C1). `spine.ts:122` renders `process.env.CONDUCTOR_MODEL` into the report header
(C14). `spine.ts:73` — contracts injected via the step closure, in-process (C11).
23 personas confirmed at `conductor/agents/*.md`.

**Rejected alternatives.**
- A `@boocode/conductor` workspace package — rejected: only two consumers (Phase-1
  CLI + coder); a shared package is premature abstraction (YAGNI). Deferred with a
  reopen trigger (a 3rd app needing conductor types). See Deferred (YAGNI).
- Importing `conductor/src/*` directly from `apps/coder` across the workspace
  boundary — rejected: couples the coder build to the standalone CLI tree and its
  `opencode`-flavored dispatch import graph.

**Specialist owner.** software-architect.
**Revisit criterion.** A third app needs the conductor types (then extract the
workspace package).
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Re-home & DispatchFn seam; tasks.md group 1.

---

## D-2 — DB-driven flow-runner with an `onTaskTerminal` dispatcher hook

**Decision.** Add `apps/coder/src/services/flow-runner.ts`: a DB-backed scheduler
that owns `flow_runs`/`flow_steps`, computes the ready wave from the loaded flow
def, INSERTs each ready `agent` step as a `tasks` row, runs `code` steps inline,
and advances. Fan-out is driven by ONE new hook — an `onTaskTerminal(taskId,
state)` callback on `createDispatcher` — invoked when any task reaches a terminal
state. No third poll loop; no modification to the dispatcher's internal run
functions.

**Rationale.** The dispatcher already has the LISTEN/NOTIFY + poll machinery and
the terminal-state transitions; a single callback at those transition points lets
the flow-runner react without duplicating the dispatch loop. The flow-runner stays
a pure scheduler; execution stays in the dispatcher.

**Evidence.** `dispatcher.ts:46-179` (the loop + `runTask`), `:279-286` (the
`notify_tasks_new` trigger) (C2). Terminal transitions the hook attaches to:
external completed `dispatcher.ts:642-646`, external failed `:659-661`. Full step
output must persist in `flow_steps.output TEXT` because `tasks.output_summary` is
≤500 char and cannot reconstruct `ctx.results` for render/resume (`schema.sql:26`,
`flow.ts:49,59`) (C3).

**Rejected alternatives.**
- A standalone third poll loop in the flow-runner — rejected: duplicates the
  dispatcher's LISTEN/poll, two writers racing on `tasks`.
- Modifying the dispatcher's `runTask` internals to know about flows — rejected:
  couples the generic dispatcher to the orchestrator; the callback seam keeps the
  dispatcher flow-agnostic.

**Specialist owner.** software-architect.
**Revisit criterion.** Step throughput requires batching beyond what one callback
per terminal task supports.
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Flow-runner & onTaskTerminal; tasks.md group 4.

---

## D-3 — Reuse the existing dispatcher (insert pending task), not a direct-PTY bypass

**Decision.** The flow-runner INSERTs each ready step as a normal `state='pending'`
`tasks` row; the existing dispatcher picks it up via `LISTEN 'tasks_new'`, runs it
through the existing external-agent path (creating a git worktree as a stable HEAD
read-checkout), and streams AgentEvents → WS frames unchanged. The new
`onTaskTerminal` hook (D-2) notifies the flow-runner on terminal state. No
direct-PTY bypass; the dispatcher is reused with exactly one new hook.

This **REVISES design-context decision 5** ("no worktree") to: a worktree IS
created, but it is a harmless read snapshot — read-only is enforced by plan mode
(D-4), not by the absence of a worktree.

**Rationale.** Reuse (architect's A2) gets streaming, persistence, resume,
cancellation, and AgentEvent→WS mapping for free. The only objection to A2 was
that it creates a worktree the "no worktree" decision-5 wanted to avoid; once
read-only is enforced at the tool level by plan mode (D-4), the worktree is inert
(a checkout the agent cannot write to), so the objection dissolves. This was the
user's explicit choice over the architect's leaning-toward-bypass (A4).

**Evidence.** The external-agent path with worktree creation and AgentEvent→WS
streaming: `dispatcher.ts` external branch (worktree create → run → terminal at
`:642-646`/`:659-661`). Task-as-dispatch precedents the flow-runner copies:
`routes/skills.ts:94` (a skill is already dispatched as a task),
`routes/arena.ts:49`, `tools/new_task.ts:54`. Dispatch tension recorded as C12
(A2 vs A4, architect self-flagged Disputed); resolved here by user choice.

**Rejected alternatives.**
- A4 direct-`dispatchViaPty` bypass (insert `running` task + call PTY directly to
  skip worktree creation) — rejected: duplicates streaming/persistence/resume
  wiring, and a restart kills the PTY child outside the dispatcher's lifecycle
  (worsening resume, C15). The worktree it was avoiding is harmless under D-4.
- design-context decision 5's "no worktree, read project dir directly" — rejected:
  reusing the dispatcher means reusing its worktree creation; under D-4 the
  worktree is a read snapshot, so avoiding it bought nothing and cost the reuse.

**Specialist owner.** software-architect (execution path); devops-engineer
(operational behavior of the reused dispatcher under flow load).
**Revisit criterion.** Worktree creation per step becomes a measured throughput or
disk-cost problem under real flow concurrency.
**Driven by rounds:** R1 (C12), R2 (read-only finding that made the worktree inert).
**Referenced in plan:** design.md §Execution via dispatcher reuse; tasks.md group 4.

---

## D-4 — Read-only enforced HARD by `mode_id='plan'` (qwen `--approval-mode plan`)

**Decision.** Every orchestrator step task is dispatched with `mode_id = 'plan'`,
which the PTY dispatcher passes to qwen as `--approval-mode plan` — a built-in
tool-level gate: reads allowed, writes blocked. The flow-runner hardcodes
`mode_id='plan'` for every step task; it is never user-overridable. This is the
sole read-only enforcement mechanism. `BOOCODE_TOOLS` and persona prompts are NOT
relied upon (they do not govern external CLI agents).

**Rationale.** Read-only is a safety-critical invariant of the whole feature
(flows never write the repo). Prompt-level intent and `BOOCODE_TOOLS` ceilings
govern BooChat's in-process tools, not an external `qwen` CLI child — so they are
not watertight. qwen's `--approval-mode plan` is a tool-level gate inside the
agent binary itself, which the adversarial-security-analyst (R2) identified as the
only enforcement that actually binds the external agent. Qwen-only (decision 6)
makes a single hardcoded flag sufficient.

**Evidence.** The wiring already exists: `pty-dispatch.ts:75` —
`if (modeId) args.push('--approval-mode', modeId)` in the `qwen` spawn spec. R2
security finding recorded as C13 (the R1 claim that prompt-level + `BOOCODE_TOOLS`
enforcement was sufficient was Anecdotal/unproven; R2 refuted it and named plan
mode as the binding control).

**Rejected alternatives.**
- Prompt-level read-only intent (personas tell the agent not to write) — rejected
  (C13, R2): an instruction, not a gate; a model can ignore or be steered past it.
- `BOOCODE_TOOLS=core` as the gate — rejected (C13, R2): governs BooChat's
  in-process tool registry, does not constrain the external `qwen` CLI's own tools.
- A `read_only` boolean flag on `tasks` — rejected: superseded by `mode_id='plan'`,
  which is an existing column already plumbed to the binary. See Deferred (YAGNI).

**Specialist owner.** adversarial-security-analyst.
**Revisit criterion.** A non-qwen agent is added to flows (re-verify that agent's
equivalent of `--approval-mode plan` before allowing it), or qwen changes
`--approval-mode plan` semantics.
**Driven by rounds:** R1 (C13 flagged), R2 (resolved).
**Referenced in plan:** design.md §Read-only via plan mode; tasks.md group 4.

---

## D-5 — `flow_runs` + `flow_steps` schema in the coder schema

**Decision.** Add two tables to `apps/coder/src/schema.sql`:

- `flow_runs(id, project_id [no FK, matches tasks.project_id], flow_name, band
  [CHECK small|medium|large], model, status [CHECK-named], input JSONB
  [CHECK (input ? 'question')], report TEXT [nullable], error, timestamps)`.
- `flow_steps(id, run_id [FK → flow_runs ON DELETE CASCADE], step_id, kind
  [CHECK agent|code], agent, status [CHECK-named], task_id [UUID → tasks(id) ON
  DELETE SET NULL; nullable, code steps NULL], chat_id [UUID → chats(id) ON DELETE
  SET NULL], input TEXT, output TEXT [FULL output], error, timestamps, UNIQUE(run_id,
  step_id))`.

No `depends_on` column (derive from the loaded flow def). Do NOT insert
skipped-step rows (`when()` is pure on stored input). Indexes:
`flow_steps(run_id, status)`, `flow_runs(project_id, created_at DESC)`. Explicit
CHECK constraint names + the repo's DROP-IF-EXISTS → guarded-ADD migration
discipline.

**Rationale.** A run spans multiple tasks; existing tables (`tasks`,
`agent_sessions`) model single dispatches, not a DAG. `flow_steps.task_id →
tasks(id)` (not a column on `tasks`) keeps `tasks` generic. `output TEXT` is FULL
because `tasks.output_summary` is ≤500 char and cannot reconstruct `ctx.results`.
`project_id` has no FK to match `tasks.project_id`'s existing convention.

**Evidence.** `tasks` shape and `output_summary` ≤500 char: `schema.sql:18-34`,
`:26` (C3, C4). `flow.ts:49,59` (results reconstruction needs full output, C3).
`flow.ts:28-41`, `types.ts:27` (deps + `when()` derivable from flow def — omit
`depends_on` and skipped rows, C6). `schema.sql:19,32` (project_id no-FK pattern;
CHECK-named discipline, C5). Migration discipline: root CLAUDE.md schema section.

**Rejected alternatives.**
- A `depends_on` column on `flow_steps` — rejected (C6, YAGNI): deps are in the
  loaded flow def; storing them duplicates the source of truth. Deferred.
- Persisting skipped-step rows — rejected (C6, YAGNI): `when()` is pure on stored
  `input`, so a skip is reconstructable. Deferred.
- A column on `tasks` (e.g. `flow_step_id`) — rejected (C4): pollutes the generic
  tasks table; the FK belongs on `flow_steps`.

**Specialist owner.** data-engineer.
**Revisit criterion.** A stored-run DAG visualization needs deps without loading
the flow def (then add `depends_on`); the UI must explain a skip without the flow
def (then persist skipped rows).
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Schema; tasks.md group 2.

---

## D-6 — Two new WS frames; per-agent stream reuses existing frames by `chat_id`

**Decision.** Add two frames to `packages/contracts/src/ws-frames.ts`:

- `flow_run_started`: `run_id, flow_name, band, steps[]` (each `step_id, agent,
  kind, chat_id, label`).
- `flow_run_step_updated`: `run_id, step_id, status, run_status?, report?`.

The per-agent content stream REUSES the existing `delta` / `tool_call` /
`message_complete` frames keyed by the step's `chat_id`. Each agent step gets a
synthetic `chats` row for stream attribution. Register in all THREE frame
registries: contracts `WsFrameSchema`, the server `InferenceFrame` union
(`services/inference/turn.ts`), and the web strict `WsFrame` union
(`apps/web/src/api/types.ts`) — the web type is the wire-format gate.

**Rationale.** The run-level lifecycle (which agents exist, their status, the final
report) needs new frames; the per-agent token stream is exactly what the existing
delta/tool_call/message_complete pipeline already carries, so keying it by a
synthetic `chat_id` reuses the whole broker→WS path with no new streaming code.
The report rides on `flow_run_step_updated` rather than its own frame (one fewer
frame type; revisit only if reports exceed the frame size limit).

**Evidence.** Existing broker→WS frame pipeline and frame list: `ws-frames.ts`
(snapshot…error). Three-registry rule + web-type-is-wire-gate: root CLAUDE.md
"Adding a new WS frame type" + discovery notes §packages/contracts. Stream-by-chat
reuse precedent: the dispatcher publishes delta/tool_call/message_complete keyed
by chat already (C7).

**Rejected alternatives.**
- New per-agent stream frames (`flow_agent_delta`, etc.) — rejected: the existing
  delta/tool_call/message_complete already stream by chat; new frames duplicate
  them.
- A separate `flow_run_report` frame — rejected (YAGNI): the report fits on
  `flow_run_step_updated`. Deferred with a reopen trigger (reports exceed ~50KB).

**Specialist owner.** software-architect.
**Revisit criterion.** Reports exceed the frame size limit (~50KB) → split the
report onto its own frame.
**Driven by rounds:** R1.
**Referenced in plan:** design.md §WS frames; tasks.md group 3.

---

## D-7 — `orchestrator` pane kind + OrchestratorPane

**Decision.** Add an `orchestrator` pane kind (following the
`markdown_artifact`/`html_artifact` precedent) — touching `WorkspacePaneKind`,
`useWorkspacePanes`, `Workspace`, `NewPaneMenu`, `ChatTabBar`,
`PaneHeaderActions`. `OrchestratorPane.tsx`: run header; report-at-top on
completion; collapsed agent roster reusing `AgentStatusDot`; expand-one-at-a-time
detail well reusing CoderPane stream rendering; mobile single-column inline
expand; auto-expand-follows-active. Runs history in `NewPaneMenu`. Export (copy /
save-file / send-to-chat via the existing `sendToChat`) in the pane header `…`,
conditional on a completed report.

**Rationale.** A fourth pane kind is already a precedented extension point; the
pane reuses `AgentStatusDot` and the CoderPane stream renderer, so the new surface
is composition, not new streaming UI. Expand-one-at-a-time avoids the crowding the
grill rejected.

**Evidence.** Pane-kind precedent: `api/types.ts:386` `WorkspacePaneKind` (with
`markdown_artifact`/`html_artifact`). Roster/status reuse: `AgentComposerBar.tsx:204`
(`AgentStatusDot`), CoderPane stream rendering (C8). Launcher categories from the
flow registry: `flows/index.ts`; runs history host `NewPaneMenu.tsx`; export via
`lib/events.ts` `sendToChat` (C10).

**Rejected alternatives.**
- Rendering runs inside the existing `coder` pane — rejected: a run is a
  parent-with-nested-children view, not a single agent session; conflating them
  crowds both.
- All-agents-expanded simultaneously — rejected (C8): the crowding the design
  session explicitly rejected.

**Specialist owner.** user-experience-designer.
**Revisit criterion.** Users cannot follow multiple concurrent runs from the
roster (then revisit the expand model).
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Orchestrator pane; tasks.md groups 7, 10.

---

## D-8 — Workflow toolbar button + slash launch, BooChat/BooCoder parity

**Decision.** Add a `Workflow` (lucide) button on `ChatInput`'s controls row,
between the `SquareSlash` chip and the `Globe` pill — yielding parity in BooChat
(ChatPane) and BooCoder (CoderPane) for free. Label "Flows" on desktop, icon-only
on mobile (toolbar confirmed to fit one line). Slash launches instantly with
defaults (band small, current pane's project, text-after-command = focus),
opening the pane. The button opens `FlowLauncherDialog.tsx` first: 5 category tabs
(Analysis/Discovery/Planning/Authoring/Review) → filtered flow list + size + focus
+ fast toggle; defaults Analysis/Small/off.

**Rationale.** `ChatInput` is the shared composer rendered by both panes, so a
single button gives both doors with parity at no extra cost. The toolbar fits one
line at ≤5 elements, so adding the button does not force scroll/wrap (a standing
mobile constraint).

**Evidence.** `ChatInput.tsx:648-732`, `:673` — the controls row is ≤5 elements;
adding the `Workflow` icon between SquareSlash and Globe keeps it one line; refutes
junior Q13's crowding worry (C9). Launcher categories from `flows/index.ts` (C10).
Shared-composer fact: discovery notes §apps/web (ChatInput rendered by ChatPane +
CoderPane).

**Rejected alternatives.**
- Separate buttons in ChatPane and CoderPane — rejected: duplicates wiring; the
  shared composer already gives parity from one button.
- A launcher search box instead of category tabs — rejected (YAGNI): 22 flows in 5
  categories are browsable; a search box is unproven need. Deferred.

**Specialist owner.** user-experience-designer.
**Revisit criterion.** Category grouping fails users at the 22-flow catalog size
(then add the search box).
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Toolbar button & launcher; tasks.md groups 8, 9.

---

## D-9 — Resumable runs via `initResume` on coder startup

**Decision.** On coder startup, an `initResume` re-advances every `flow_runs WHERE
status='running'`: a step whose task completed → mark the step done + advance the
run; a step whose task is lost/failed (PTY died on restart) → re-dispatch;
completed steps are kept. (design-context decision 4 commits to "resumable".)

**Rationale.** A restart can land mid-flight. Because execution goes through the
dispatcher with persisted task state (D-3), a step's outcome is recoverable from
the DB; the run-level scheduler just has to re-derive the wave and re-dispatch only
the steps that did not finish. Reconcile-and-advance (architect A3) beats
mark-run-failed (data's conservative option) because decision 4 already committed
to resumable and the task state is durable.

**Evidence.** No run-level resume exists today (single tasks resume via
`agent_sessions`; a run spanning tasks does not) — discovery notes §Enumerated
gaps. Resume tension recorded as C15 (architect reconcile-and-advance vs data
mark-failed); resolved toward reconcile-and-advance by decision 4 + durable task
state under D-3.

**Rejected alternatives.**
- Mark a running run failed on restart — rejected (C15): contradicts decision 4
  (resumable) and discards recoverable completed-step work.
- Re-running the whole flow from step 0 — rejected: re-does completed steps,
  burning the local model on work already persisted.

**Specialist owner.** software-architect (scheduler); data-engineer (recovery query).
**Revisit criterion.** A step-level idempotency hazard surfaces where re-dispatch
of a "lost" step double-counts side effects (none expected under read-only plan
mode).
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Resume; tasks.md group 5.

---

## D-10 — Concurrency: multiple runs, no `queued` status, single model per run

**Decision.** Multiple runs are allowed; each gets its own pane + `flow_runs` row,
no shared state. Step statuses are pending / running / completed / failed / skipped
— there is NO separate `queued` status (the dispatcher's `pending` covers a step
waiting on the busy model or on deps). Model is a single config value per run,
default `qwen3.6-35b-a3b-mxfp4`.

**Rationale.** Each run is independent state, so concurrency needs no coordination
beyond the dispatcher's existing per-session serialization. A `queued` status is
not observable: with the model busy, a task is simply `pending`/`running` and
llama-swap does not expose queue position, so a distinct `queued` state would be a
label the system cannot honestly populate (revising decision-11's "panes show
queued honestly").

**Evidence.** `queued` unobservability recorded as C16 (junior Q11, data
DATA-005): llama-swap does not report queue position; the status reduces to
pending(dep/model-wait)/running. Single-model-per-run carried from decision 6/11.

**Rejected alternatives.**
- A distinct `queued` step status — rejected (C16): nothing can populate it
  honestly; `pending` already means "waiting". Deferred (reopen if llama-swap
  exposes queue position).
- Serializing runs (one at a time) — rejected: runs are independent; serialization
  adds coordination for no benefit and hurts the multi-pane UX (decision 11).

**Specialist owner.** data-engineer (status set), devops-engineer (model-busy
behavior under concurrent runs).
**Revisit criterion.** llama-swap exposes queue position → add an observable
`queued` status.
**Driven by rounds:** R1.
**Referenced in plan:** design.md §Schema (status sets) + §Concurrency; tasks.md
group 2.

---

## Cross-reference index

| Decision | Driven by | Design.md section | Tasks.md group |
|---|---|---|---|
| D-1 Re-home + DispatchFn | R1 (C1, C11, C14) | Re-home & DispatchFn seam | 1 |
| D-2 Flow-runner + onTaskTerminal | R1 (C2, C3) | Flow-runner & onTaskTerminal | 4 |
| D-3 Dispatcher reuse (not bypass) | R1 (C12), R2 | Execution via dispatcher reuse | 4 |
| D-4 Read-only via plan mode | R1 (C13), R2 | Read-only via plan mode | 4 |
| D-5 Schema flow_runs/flow_steps | R1 (C3–C6) | Schema | 2 |
| D-6 WS frames | R1 (C7) | WS frames | 3 |
| D-7 Orchestrator pane | R1 (C8) | Orchestrator pane | 7, 10 |
| D-8 Toolbar button + slash | R1 (C9, C10) | Toolbar button & launcher | 8, 9 |
| D-9 Resume | R1 (C15) | Resume | 5 |
| D-10 Concurrency / no-queued | R1 (C16) | Schema + Concurrency | 2 |

## Deferred (YAGNI)

These were considered and deferred under the evidence rule. Each names the trigger
that would justify reopening.

### `@boocode/conductor` workspace package
- **Why deferred:** only two consumers (Phase-1 CLI + coder); copy-in (D-1) avoids
  premature shared-package abstraction.
- **Reopen when:** a third app needs the conductor types.
- **Source:** architect (D-1 rejected alternative).

### `flow_steps.depends_on` column
- **Why deferred:** deps are derivable from the loaded flow def (`flow.ts:28-41`,
  `types.ts:27`); a column duplicates the source of truth.
- **Reopen when:** a stored-run DAG visualization must show deps without loading
  the flow def.
- **Source:** data-engineer C6 (D-5 rejected alternative).

### Persisted skipped-step rows
- **Why deferred:** `when()` is pure on stored `input`, so a skip is
  reconstructable from the flow def + run input.
- **Reopen when:** the UI must explain a skip without the flow def.
- **Source:** data-engineer C6 (D-5 rejected alternative).

### `read_only` flag on `tasks`
- **Why deferred:** superseded by `mode_id='plan'` (D-4), an existing column
  already plumbed to qwen's `--approval-mode`.
- **Reopen when:** a non-qwen agent without a `--approval-mode plan` equivalent is
  added to flows.
- **Source:** D-4 rejected alternative.

### Explicit `queued` step status
- **Why deferred:** llama-swap does not expose queue position; nothing can populate
  the status honestly (C16). `pending` covers waiting.
- **Reopen when:** llama-swap exposes queue position.
- **Source:** junior Q11 / data DATA-005 (D-10 rejected alternative).

### Launcher search box
- **Why deferred:** 22 flows in 5 category tabs are browsable; a search box is
  unproven need.
- **Reopen when:** category grouping fails users at the catalog size.
- **Source:** UX C10 (D-8 rejected alternative).

### Separate report-stored WS frame
- **Why deferred:** the report rides on `flow_run_step_updated` (D-6).
- **Reopen when:** reports exceed the ~50KB frame size limit.
- **Source:** architect C7 (D-6 rejected alternative).
