The last batch of outstanding work from the agents audit (after #1460,
#1475, #1483): the section-3 dead-code sweep and the UI shrink. Net
**−188 lines** (−503/+315).

## One agent setup form

`agents/new.tsx` and `agents/new-preset.tsx` were ~270-line,
~90%-identical forms (provider/model/runOpts/system-prompt/custom-events
fields plus the YAML preview pane). They now share one
`AgentSetupFormPage` component; each route keeps only what genuinely
differs — its path normalization, its preview builder, and its submit
mutation:

```tsx
<AgentSetupFormPage
  title="New Agent"
  pathLabel="Agent path"
  buildPreview={(values) => buildPreviewEvents({ projectId: project.id, values })}
  submitIdleLabel="Create agent"
  isPending={createAgent.isPending}
  onSubmit={({ preview }) => createAgent.mutate(preview)}
  ...
/>
```

The routes drop from ~270 lines each to ~125, and the next form tweak
happens once instead of twice.

## Legacy Slack preset filter deleted

`agent-presets.ts` carried `isLegacyGeneratedSlackOpenAiPreset` — a
content-sniffing filter that suppressed an old auto-generated
`/agents/slack` preset by matching its system-prompt text. Checked prd
before deleting: the iterate project has **zero** stored presets, so the
filter guards nothing. The intentional behavior next to it (Slack agents
never inherit the generic `/agents` preset) stays, with its tests.

## Stale migration headers

Every processor under
`apps/os/src/domains/{agents,slack}/stream-processors/` opened with
"Migrated from `packages/shared/src/stream-processors/...`" — a
directory that no longer exists. Those provenance paragraphs are gone.
Where they carried a live constraint, the constraint survives in its own
words:

```ts
// Appended event types, payload shapes, and idempotency-key derivations
// (`agent/<key>@<sourceOffset>`) are stable wire formats — changing them
// breaks dedup against events already committed to streams.
```

## Audit bug status (no code change needed)

- **2.4 zombie `pendingTriggerCount`** — fixed by construction since
#1460: the reconcilers guarantee dangling requests reach a terminal
event, and a queued count only ever represents real user inputs whose
follow-up turn rebuilds from full history.
- **2.3 cancellation check-then-act race** — still a theoretical window;
closing it needs conditional appends (append-if-still-current at the
stream layer), which is its own design, not a cleanup.

`pnpm typecheck && pnpm lint && pnpm format && pnpm test` all green.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Mostly UI deduplication and comment edits; Slack preset selection is
slightly broader if old auto-generated presets exist in storage, which
the PR assumes is empty.
> 
> **Overview**
> Introduces **`AgentSetupFormPage`** so **New Agent** and **New Agent
Preset** share one form (provider, model, run options, system prompt,
custom events YAML, live preview). Each route only keeps path handling,
its preview builder, and submit logic—roughly halving page size.
> 
> **Removes** the legacy **`isLegacyGeneratedSlackOpenAiPreset`** filter
and its test from `agent-presets.ts`. Slack agents still only match
Slack-scoped presets; stored `/agents/slack` presets are no longer
sniffed and ignored by prompt text.
> 
> **Trims** stale “migrated from `packages/shared`…” headers across
agent and Slack stream-processor modules, leaving short notes where wire
formats and idempotency keys must stay stable.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
c9cf738. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

<!-- CLOUDFLARE_PREVIEW -->
## Environment Config Lease
<!-- CLOUDFLARE_PREVIEW_STATE -->
<!--
{
  "apps": {
    "os": {
      "appDisplayName": "OS",
      "appSlug": "os",
      "status": "deployed",
      "updatedAt": "2026-06-10T22:24:45.981Z",
      "headSha": "c9cf738e2dad4877de8286cf370cf50cedd81eeb",
      "message": null,
      "publicUrl": "https://os.iterate-preview-4.com",
"runUrl": "https://github.com/iterate/iterate/actions/runs/27310094398",
      "shortSha": "c9cf738"
    }
  },
  "environmentConfigLease": {
    "dopplerConfig": "preview_4",
    "leasedUntil": 1781133683378,
    "leaseId": "51ccdfaf-05f8-4f1c-a8ed-1b26dec7500b",
    "slug": "preview-4",
    "type": "environment-config-lease"
  }
}
-->
<!-- /CLOUDFLARE_PREVIEW_STATE -->
Lease: `preview-4`
Doppler config: `preview_4`
Type: `environment-config-lease`
Leased until: 2026-06-10T23:21:23.378Z

### OS
Status: deployed
Commit: `c9cf738`
Preview: https://os.iterate-preview-4.com
[Workflow
run](https://github.com/iterate/iterate/actions/runs/27310094398)
Updated: 2026-06-10T22:24:45.981Z
<!-- /CLOUDFLARE_PREVIEW -->

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Post-merge grooming after the agents workstream landed (#1460, #1475,
#1483, #1484). Grooming rules (docs/tasks-grooming.md) say tasks are
deleted when done:

- **Deleted** `tasks/streams-core-processor-host-homogenization.md` —
the plan of record for what shipped in #1460.
- **Deleted** `tasks/agents-system-audit-and-reconciler-design.md` — the
audit knowledge dump; every verified bug and design direction in it is
now either shipped or carried by a live task file.
- **Updated** the two deferred follow-ups
(`streams-core-clock-durable-timers.md`,
`streams-event-kinds-metadata.md`) to drop their `dependsOn`/background
references to the deleted docs, pointing at the merged PRs instead.
- **Added** `tasks/streams-conditional-appends.md` — the one audit
finding that survived everything: the check-then-act window between a
provider's still-current check and its `agent/output-added` append.
Backlog, with the conditional-append direction written down so it isn't
lost with the audit doc.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Documentation-only changes under `tasks/` with no runtime or API
impact.
> 
> **Overview**
> **Grooms the `tasks/` backlog** after agents/streams work landed in
#1460 and related PRs, per `docs/tasks-grooming.md` (delete tasks when
done).
> 
> **Removes** the shipped plan-of-record
(`streams-core-processor-host-homogenization.md`) and the umbrella
audit/knowledge dump (`agents-system-audit-and-reconciler-design.md`),
since their content is either merged or split elsewhere.
> 
> **Refreshes** deferred follow-ups:
`streams-core-clock-durable-timers.md` and
`streams-event-kinds-metadata.md` drop `dependsOn` on deleted tasks and
cite PR #1460 in background instead of dead links.
> 
> **Adds** `streams-conditional-appends.md` (backlog) to capture the
remaining audit item—the LLM output **check-then-act** race—and the
direction (stream-level conditional append / CAS), so it isn’t lost with
the audit doc.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
d9b9d7f. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>