hashintel · kostandinang · May 14, 2026 · May 14, 2026 · May 14, 2026 · May 14, 2026
diff --git a/HANDOFF.md b/HANDOFF.md
@@ -1,46 +1,76 @@
 # Handoff
 
-> Generated by `ln-handoff` at 2026-05-13. Read this file to resume work.
+> Generated by `ln-build` at 2026-05-14. Read this file to resume work.
 > This file is volatile transfer state only. After its contents are reconciled into canonical docs or superseded by a newer handoff, overwrite or delete it.
 
 ## Goal
 
-Ship the continuous workspace shell (FE-709) — cumulative phase sections, one chat runtime, sidebar scroll-spy, preserved phase addressability.
+Land the **thread substrate** for FE-710 (chat-runtime-threads) and advance to the next slice.
 
 ## Session State
 
-- **Last completed skill**: `ln-build` — Steps 1–4 of CONTINUOUS_WORKSPACE_HYBRID.md migration plan + helper extraction all committed
-- **Flow position**: `plan → scope → build (×3) → handoff → review → scope → build (helper extraction) → scope → build (Step 4) → ready for PR`
+- **Last completed skill**: `ln-build` — substrate-landing slice implemented and verified (1261/1261 tests, full `npm run verify` gate passed).
+- **Before that**: prior session ran `ln-design` → `ln-scope` → `ln-spec` → `ln-handoff`; produced the scope card, settled D153/D154/A94, opened PR #138 with the planning baseline.
+- **Flow position**: `design → scope → spec → handoff → build (done) → [scope next slice]`
 
-## Commits on branch (6 total)
+## What landed
 
-1. `ed183421` FE-709: Plan umbrella frontier items + assign continuous-workspace
-2. `372bba97` FE-709: Replace per-phase InterviewView with ContinuousWorkspaceView
-3. `fa712f54` FE-709: Extract useContinuousWorkspaceController
-4. `5292dbfb` FE-709: Sidebar scroll-spy highlighting via WorkspaceFocusContext
-5. `f60eac9` FE-709: Extract shared controller helpers and enrichBottomArtifact to core
-6. `7a35eee` FE-709: Retire route-first test assumptions
+### Migration 0020 — thread substrate
 
-## Remaining work
+- `drizzle/0020_thread_substrate.sql` + journal entry
+- Created `thread` table: `id`, `chat_id`, `kind` (interview/side/reconciliation/qa/agent_run), `target_item_id`, `context_spec`, `kickoff_turn_id`, `invoked_in_turn_id`, `active_turn_id`, `status`, `created_at`
+- Partial unique index `thread_interview_unique` on `(chat_id) WHERE kind = 'interview'`
+- Migrated `turn.chat_id` → `turn.thread_id` (NOT NULL)
+- Dropped `chat.kind` and `chat.active_turn_id` (chat is now a pure container)
+- Data migration: seeded one interview thread per existing chat; mapped turn rows through thread join
 
-### Step 5 — Route collapse decision (DEFERRED)
+### Schema (`src/server/schema.ts`)
 
-Per CONTINUOUS_WORKSPACE_HYBRID.md §Migration Step 5: decide whether phase routes should become redirects or search-param aliases. This is a design decision, not urgent — the continuous center pane works correctly with current routes. Phase routes currently act as focus addresses into the shared workspace surface, which is the intended hybrid behavior.
+- Added `thread` table definition with all columns and partial unique index
+- Removed `kind` and `active_turn_id` from `chat`
+- Changed `turn.chat_id` → `turn.thread_id` (NOT NULL, FK to thread)
 
-### PR submission
+### Specification store (`src/server/db/specification-store.ts`)
 
-Branch `ka/fe-709-continuous-workspace` is ready for `gt submit`. All steps are complete except the deferred design decision (Step 5).
+- `insertSpecificationWithInterviewChat` now creates spec + chat + interview thread atomically
+- Added `getInterviewThreadIdForSpecification` helper
+- `createTurn` routes through interview thread (validates parent in same thread)
+- `advanceHead` mirrors `active_turn_id` to interview thread (was chat)
 
-## Test status
+### Capabilities (`src/server/capabilities.ts`)
 
-1213/1214 pass. 1 pre-existing flake in InterviewView.test.tsx (`renders live workspace-tool activity during the submitted pre-stream generating window` — tool detail assertion, unrelated to FE-709).
+- `getChatById` now joins through thread to source `kind` and `active_turn_id` from interview thread
+- `getPrimaryChatFromCapability` delegates to updated `getChatById`
+- `submitTurnResponseFromCapability` validates turn ownership through `specification_id` (was `chat_id`)
 
-## Open questions (unchanged from prior handoff)
+### Tests (`src/server/chat-substrate.test.ts`)
 
-- Should the sticky center-pane header update to show the *focused* (scrolled-to) phase rather than always the *active* phase? Deferred to UX review.
-- IntersectionObserver thresholds may need tuning for short sections. Manual walkthrough showed no issues.
-- Should deep-link target become `?phase=design` search param or keep legacy phase paths? Deferred to Step 5.
+- Full rewrite: 14 tests covering schema assertions, atomic quad creation, thread uniqueness, turn writes, head mirroring, atomicity, and read-path equivalence
+
+### Blast-radius fixes
+
+- `src/server/context.test.ts` — turn fixtures updated `chat_id: null` → `thread_id: 0`
+
+## Decisions and assumptions
+
+| Item | Type | Status | Source |
+| --- | --- | --- | --- |
+| Eager interview-thread creation in createSpecification | assumption | validated | scope card → code proves it |
+| `chat.kind` and `chat.active_turn_id` retire entirely | decision | validated | grep clean; no readers remain |
+
+## Repo state
+
+- **Branch**: `ka/fe-710-chat-runtime-threads`
+- **PR**: #138 (open, planning baseline only)
+- **Dirty files**: all substrate changes uncommitted (ready for commit)
+- **Test status**: 1261/1261 passing; `npm run verify` gate clean
+
+## Next steps
+
+1. Commit the substrate-landing slice on the current branch.
+2. Scope the next slice: in-stream collapsible UI for non-interview thread kinds + `SideChatPopover` retirement cutover. This is still inside FE-710; same branch.
+3. Manual walkthrough: `npm run dev`, create a spec, advance through a few grounding turns, reload, confirm continuity.
 
 ## Retirement rule
 
-Delete this file after PR is submitted or after Step 5 is decided.
+- Overwrite or delete this file once the next slice is scoped and the substrate commit is verified.
diff --git a/drizzle/0020_thread_substrate.sql b/drizzle/0020_thread_substrate.sql
@@ -0,0 +1,64 @@
+-- 1. Create thread table
+CREATE TABLE `thread` (
+	`id` integer PRIMARY KEY AUTOINCREMENT NOT NULL,
+	`chat_id` integer NOT NULL,
+	`kind` text NOT NULL,
+	`target_item_id` integer,
+	`context_spec` text,
+	`kickoff_turn_id` integer,
+	`invoked_in_turn_id` integer,
+	`active_turn_id` integer,
+	`status` text DEFAULT 'open' NOT NULL,
+	`created_at` text DEFAULT (datetime('now')) NOT NULL,
+	FOREIGN KEY (`chat_id`) REFERENCES `chat`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`target_item_id`) REFERENCES `knowledge_item`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`kickoff_turn_id`) REFERENCES `turn`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`invoked_in_turn_id`) REFERENCES `turn`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`active_turn_id`) REFERENCES `turn`(`id`) ON UPDATE no action ON DELETE no action
+);--> statement-breakpoint
+
+-- 2. Partial unique index: exactly one interview thread per chat
+CREATE UNIQUE INDEX `thread_interview_unique` ON `thread` (`chat_id`) WHERE kind = 'interview';--> statement-breakpoint
+
+-- 3. Seed one interview thread per existing chat
+INSERT INTO `thread` (`chat_id`, `kind`, `active_turn_id`)
+SELECT `id`, 'interview', `active_turn_id` FROM `chat`;--> statement-breakpoint
+
+-- 4. Recreate turn with thread_id instead of chat_id
+CREATE TABLE `turn_new` (
+	`id` integer PRIMARY KEY AUTOINCREMENT NOT NULL,
+	`specification_id` integer NOT NULL,
+	`thread_id` integer NOT NULL,
+	`parent_turn_id` integer,
+	`phase` text NOT NULL,
+	`turn_kind` text DEFAULT 'question' NOT NULL,
+	`question` text DEFAULT '' NOT NULL,
+	`why` text,
+	`impact` text,
+	`answer` text,
+	`is_resolution` integer DEFAULT false NOT NULL,
+	`user_parts` text,
+	`assistant_parts` text,
+	`created_at` text DEFAULT (datetime('now')) NOT NULL,
+	FOREIGN KEY (`specification_id`) REFERENCES `specification`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`thread_id`) REFERENCES `thread`(`id`) ON UPDATE no action ON DELETE no action,
+	FOREIGN KEY (`parent_turn_id`) REFERENCES `turn_new`(`id`) ON UPDATE no action ON DELETE no action
+);--> statement-breakpoint
+INSERT INTO `turn_new` (`id`, `specification_id`, `thread_id`, `parent_turn_id`, `phase`, `turn_kind`, `question`, `why`, `impact`, `answer`, `is_resolution`, `user_parts`, `assistant_parts`, `created_at`)
+SELECT t.`id`, t.`specification_id`, th.`id`, t.`parent_turn_id`, t.`phase`, t.`turn_kind`, t.`question`, t.`why`, t.`impact`, t.`answer`, t.`is_resolution`, t.`user_parts`, t.`assistant_parts`, t.`created_at`
+FROM `turn` t
+JOIN `thread` th ON th.`chat_id` = t.`chat_id` AND th.`kind` = 'interview';--> statement-breakpoint
+DROP TABLE `turn`;--> statement-breakpoint
+ALTER TABLE `turn_new` RENAME TO `turn`;--> statement-breakpoint
+
+-- 5. Recreate chat without kind and active_turn_id
+CREATE TABLE `chat_new` (
+	`id` integer PRIMARY KEY AUTOINCREMENT NOT NULL,
+	`specification_id` integer NOT NULL,
+	`created_at` text DEFAULT (datetime('now')) NOT NULL,
+	FOREIGN KEY (`specification_id`) REFERENCES `specification`(`id`) ON UPDATE no action ON DELETE no action
+);--> statement-breakpoint
+INSERT INTO `chat_new` (`id`, `specification_id`, `created_at`)
+SELECT `id`, `specification_id`, `created_at` FROM `chat`;--> statement-breakpoint
+DROP TABLE `chat`;--> statement-breakpoint
+ALTER TABLE `chat_new` RENAME TO `chat`;
diff --git a/drizzle/meta/_journal.json b/drizzle/meta/_journal.json
@@ -141,6 +141,13 @@
       "when": 1776360000000,
       "tag": "0019_reconciliation_need_agent_columns",
       "breakpoints": true
+    },
+    {
+      "idx": 20,
+      "version": "7",
+      "when": 1776370000000,
+      "tag": "0020_thread_substrate",
+      "breakpoints": true
     }
   ]
 }
diff --git a/memory/PLAN.md b/memory/PLAN.md
@@ -24,16 +24,16 @@ The May 2026 intent-spec, multi-chat, changeset-ledger, prompt/context, and agen
 ### Active
 
 1. `agent-fixture-substrate` — branch-complete off main, reconciling — FE-705 integration substrate for JSONL agent capability CLI and LLM-as-user probes.
+2. `chat-runtime-threads` — FE-710; Track 2 of the runtime umbrella; substrate sub-RFC settled on option (q) new `thread` table; first slice lands the substrate without UI cutover.
 
 ### Next
 
-1. `chat-runtime-threads` — Track 2 of the runtime umbrella; immediate successor to continuous-workspace, unblocker for Tracks 3 and 5. First slice should be a sub-RFC on the thread substrate shape (p / q / r).
-2. `intent-graph-semantics` — highest-coordination semantic substrate after FE-705 reconciliation.
-3. `changeset-ledger` — Track 4 of the runtime umbrella; parallel with Track 2; semantic history spine needed before canonical proposal acceptance, direct-edit atomicity, and productized scenario options.
-4. `thread-context-provision` — Track 5 of the runtime umbrella; after Track 2 lands the thread substrate.
-5. `reconciliation-runtime` — Track 3 of the runtime umbrella; after Track 2 + Track 4 provide thread substrate and durable attribution.
-6. `graph-review-scenario-options` — artifact-only critique/probe lane; can advance in parallel with FE-700 if it does not commit canonical graph truth.
-7. `productized-scenario-options` — user-facing acceleration surface after FE-700 semantics, FE-701 changesets, and graph-review probes.
+1. `intent-graph-semantics` — highest-coordination semantic substrate after FE-705 reconciliation.
+2. `changeset-ledger` — Track 4 of the runtime umbrella; parallel with Track 2; semantic history spine needed before canonical proposal acceptance, direct-edit atomicity, and productized scenario options.
+3. `thread-context-provision` — Track 5 of the runtime umbrella; after Track 2 lands the thread substrate.
+4. `reconciliation-runtime` — Track 3 of the runtime umbrella; after Track 2 + Track 4 provide thread substrate and durable attribution.
+5. `graph-review-scenario-options` — artifact-only critique/probe lane; can advance in parallel with FE-700 if it does not commit canonical graph truth.
+6. `productized-scenario-options` — user-facing acceleration surface after FE-700 semantics, FE-701 changesets, and graph-review probes.
 
 ### Parallel / Low-conflict
 
@@ -74,15 +74,16 @@ The May 2026 intent-spec, multi-chat, changeset-ledger, prompt/context, and agen
 ### chat-runtime-threads
 
 - **Name:** Chat runtime — thread substrate + in-stream rendering (Conversational Workspace Runtime — Track 2)
-- **Linear:** unassigned in this plan snapshot
+- **Linear:** FE-710
 - **Kind:** structural
-- **Status:** not-started
-- **Objective:** Add a thread primitive to the chat substrate, render threads inline as collapsibles in the main chat surface (Cursor-style), and retire the SideChatPopover and transient staged-patches strip. Decide the thread substrate shape via a sub-RFC: (p) `parent_chat_id` on `chat`, (q) new `thread` table, or (r) UI-only rendering.
-- **Why now / unlocks:** Track 1 (workspace shell) ships, providing the stable host. Threads are the critical unblocker for reconciliation absorption into the chat surface (Track 3), `#` mention / turn-zero / context provision (Track 5), and the retirement of the V3.1 popover and staged-patches surfaces. Supersedes the prior side-chat V4a persistence horizon — persistent side-chat history becomes the main chat stream where threads stay collapsed.
-- **Acceptance:** Thread kinds (`interview`, `side`, `reconciliation`, `qa`) are representable in the substrate; threads render inline as collapsibles in the unified chat surface; SideChatPopover retires as cutover; transient staged-patches strip retires (replaced by in-thread mutation state); turn-zero (`turn_kind='kickoff'`) becomes the universal thread entry.
+- **Status:** in-progress
+- **Objective:** Add a `thread` primitive between chat and turn, render threads inline as collapsibles in the main chat surface (Cursor-style), and retire `SideChatPopover` and the transient staged-patches strip. Substrate sub-RFC settled: option (q) new `thread` table; chat collapses to a pure container; flat threads with `thread.invoked_in_turn_id` for inline agent runs (no nested threads in V1).
+- **Why now / unlocks:** Track 1 (workspace shell) shipped, providing the stable host. Threads are the critical unblocker for reconciliation absorption into the chat surface (Track 3), `#` mention / turn-zero / context provision (Track 5), changeset attribution (Track 4), and the retirement of the V3.1 popover and staged-patches surfaces. Supersedes the prior side-chat V4a persistence horizon — persistent side-chat history becomes the main chat stream where threads stay collapsed.
+- **Acceptance:** `thread` table exists with kinds (`interview`, `side`, `reconciliation`, `qa`, `agent_run`); `turn.thread_id` replaces `turn.chat_id`; `chat.kind` and `chat.active_turn_id` retire; threads render inline as collapsibles in the unified chat surface; `SideChatPopover` retires as cutover; transient staged-patches strip retires (replaced by in-thread mutation state); turn-zero (`turn_kind='kickoff'`) becomes the universal thread entry; agent runs render inline via `thread.invoked_in_turn_id`.
 - **Verification:** Thread substrate schema/migration tests, in-stream collapsible rendering tests, manual walkthroughs for thread creation/display/collapse per kind, regression on existing interview flow.
-- **Traceability:** A82, A83, A88; D86, D87, D110, D114, D138, D146; I111, I113.
+- **Traceability:** Requirements 39 (updated), 45; A88, A94; D86, D87, D110, D114, D138, D146, D153, D154; I111 (extended), I113.
 - **Design docs:** `docs/design/CONVERSATIONAL_WORKSPACE_RUNTIME.md` §3.2 + §5 Track 2; `docs/design/MULTI_CHAT.md`; `docs/design/SIDE_CHAT.md`.
+- **Current execution pointer:** substrate-landing slice landed (migration 0020, schema/store/test rewrite). Next slice: in-stream collapsible UI for non-interview thread kinds, `SideChatPopover` retirement cutover.
 
 ### reconciliation-runtime