The `/chats/{chat}/diff-status` endpoint was redundant because:
- The `Chat` type already has a `DiffStatus` field
- Listing chats already resolves and returns `diff_status`
- The `getChat` endpoint was the only one not resolving it (passing
`nil`)
## Changes
**Backend:**
- `getChat` now calls `resolveChatDiffStatus` and includes the result in
the response
- Removed `getChatDiffStatus` handler, route (`GET /diff-status`), and
SDK method
- Tests updated to use `GetChat` instead of `GetChatDiffStatus`
**Frontend:**
- `AgentDetail.tsx`: uses `chatQuery.data?.diff_status` instead of
separate query
- `RemoteDiffPanel.tsx`: accepts `diffStatus` as a prop instead of
fetching internally
- `AgentsPage.tsx`: `diff_status_change` events now invalidate the chat
query
- Removed `chatDiffStatus` query, `chatDiffStatusKey`, and
`getChatDiffStatus` API method
Adds the `head_branch` field (the source/feature branch name of a PR) to
the diff status pipeline. Previously only `base_branch` (target branch)
and the head commit SHA were captured from the GitHub API, but not the
head branch name itself.
## Changes
- **Migration 438**: Add `head_branch` nullable TEXT column to
`chat_diff_statuses`
- **gitprovider**: Parse `head.ref` from the GitHub API response
(alongside `head.sha`) and add `HeadBranch` to `PRStatus`
- **gitsync**: Wire `HeadBranch` through `refreshOne()` into the DB
upsert params
- **worker**: Map `HeadBranch` in `chatDiffStatusFromRow()`
- **coderd**: Convert `HeadBranch` in `convertChatDiffStatus()`
- **codersdk**: Expose as `head_branch` (`*string`, omitempty) in
`ChatDiffStatus` API response
- **Tests**: Updated `github_test.go` pull JSON fixtures and assertions
Surfaces cache token data in the analytics views and fixes table
spacing.
### Changes
- **Cache token columns**: Added cache read and cache write token counts
to all analytics views (user and admin), from SQL queries through Go SDK
types to the frontend tables and summary cards.
- **Table spacing fix**: Replaced the bare React fragment in
`ChatCostSummaryView` with a `space-y-6` container so the model and chat
breakdown tables no longer overlap.
### Data flow
`chat_messages` table already stores `cache_read_tokens` and
`cache_creation_tokens` (and uses them for cost calculation). This PR
aggregates and displays them alongside input/output tokens in:
- Summary cards (6 cards: Total Cost, Input, Output, Cache Read, Cache
Write, Messages)
- Per-model breakdown table
- Per-chat breakdown table
- Admin per-user table
Add cost tracking for LLM chat interactions with microdollar precision.
## Changes
- Add `chatcost` package for per-message cost calculation using
`shopspring/decimal` for intermediate arithmetic
- **Ceil rounding policy**: fractional micros round UP to next whole
micro (applied once after summing all components)
- Database migration: `total_cost_micros` BIGINT column with historical
backfill and `created_at` index
- API endpoints: per-user cost summary and admin rollup under
`/api/experimental/chats/cost/`
- SDK types: `ChatCostSummary`, `ChatCostModelBreakdown`,
`ChatCostUserRollup`
- Fix `modeloptionsgen` to handle `decimal.Decimal` as opaque numeric
type
- Update frontend pricing test fixtures for string decimal types
## Design decisions
- `NULL` = unpriced (no matching model config), `0` = free
- Reasoning tokens included in output tokens (no double-counting)
- Integer microdollars (BIGINT) for storage and API responses
- Price config uses `decimal.Decimal` for exact parsing; totals use
`int64`
Frontend: #23037
File-reference parts in user messages were flattened to `TextContent` at
write time because fantasy has no file-reference content type. The
frontend never saw them as structured parts.
This moves all write paths (user, assistant, tool) from fantasy envelope
format to `codersdk.ChatMessagePart`. The streaming layer (`chatloop`)
is untouched, the conversion happens at the serialization boundary in
`persistStep`.
Old rows are still readable. `ParseContent` uses a structural heuristic
(`isFantasyEnvelopeFormat`) to distinguish legacy envelopes from SDK
parts. We chose this over try/fallback because fantasy envelopes
partially unmarshal into `ChatMessagePart` (the `type` field matches)
while silently losing content. A guard test enforces that no SDK part
can produce the envelope shape.
This is forward-only: new rows are unreadable by old code. Chat is
behind a feature flag so rollback risk is contained.
Also adds a typed `ChatMessageRole` to replace raw strings and
`fantasy.MessageRole*` casts at the persistence boundary. The type
covers `ChatMessage.Role`, `ChatStreamMessagePart.Role`, the
`PublishMessagePart` callback chain, and all DB write sites.
`fantasy.MessageRole*` remains only where we build `fantasy.Message`
structs for LLM dispatch.
Separately, `ProviderMetadata` was leaking to SSE clients via
`publishMessagePart`. `StripInternal` now runs on both the SSE and REST
paths, covering this.
Other cleanup:
- Old `db2sdk.contentBlockToPart` silently dropped metadata on
text/reasoning/tool-call content. New code preserves it.
- `providerMetadataToOptions` now logs warnings instead of silently
returning nil.
- `db2sdk` shrinks from ~250 lines of parallel conversion to ~15 lines
delegating to `chatprompt.ParseContent()`, removing the `fantasy` import
entirely.
Refs #22821
## Summary
Moves the messages response out of `GET /chats/{id}` and into a
dedicated `GET /chats/{id}/messages` endpoint.
### Backend
- `GET /chats/{id}` now returns just the `Chat` object (no messages)
- `GET /chats/{id}/messages` is a new endpoint returning
`ChatMessagesResponse` with `messages` and `queued_messages`
- Added `ChatMessagesResponse` SDK type and `GetChatMessages` client
method
### Frontend
- `getChat()` API method returns `Chat` instead of `ChatWithMessages`
- Added `getChatMessages()` API method for the new endpoint
- Split `chatQuery` into two: `chatQuery` (metadata) and
`chatMessagesQuery` (messages)
- Updated all cache mutations, optimistic updates, and websocket
handlers
- Updated tests and stories
### Files changed
| File | Change |
|---|---|
| `coderd/coderd.go` | Register `GET /messages` route |
| `coderd/chats.go` | Simplify `getChat`, add `getChatMessages` handler
|
| `codersdk/chats.go` | New type + method, update `GetChat` return |
| `site/src/api/api.ts` | New method, update `getChat` |
| `site/src/api/queries/chats.ts` | New query, update cache mutations |
| `site/src/pages/AgentsPage/AgentDetail.tsx` | Use separate queries |
| `site/src/pages/AgentsPage/AgentDetail/ChatContext.ts` | Update types
and cache writes |
| `site/src/pages/AgentsPage/AgentsPage.tsx` | Update websocket cache
handler |
## Summary
- add chat model pricing metadata to the agents admin form and SDK
metadata
- split pricing into its own section and show default pricing as
placeholders
- apply default pricing when admins leave pricing fields blank
## What
Adds provider-native web search tools to the chat system. Anthropic,
OpenAI, and Google all offer server-side web search — this wires them up
as opt-in per-model config options using the existing
`ChatModelProviderOptions` JSONB column (no migration).
Web search is **off by default**.
## Config
Set `web_search_enabled: true` in the model config provider options:
```json
{
"provider_options": {
"anthropic": {
"web_search_enabled": true,
"allowed_domains": ["docs.coder.com", "github.com"]
}
}
}
```
Available options per provider:
- **Anthropic**: `web_search_enabled`, `allowed_domains`,
`blocked_domains`
- **OpenAI**: `web_search_enabled`, `search_context_size`
(`low`/`medium`/`high`), `allowed_domains`
- **Google**: `web_search_enabled`
## Backend
- `codersdk/chats.go` — new fields on the per-provider option structs
- `coderd/chatd/chatd.go` — `buildProviderTools()` reads config, creates
`ProviderDefinedTool` entries (uses `anthropic.WebSearchTool()` helper
from fantasy)
- `coderd/chatd/chatloop/chatloop.go` — `ProviderTools` on `RunOptions`,
merged into `Call.Tools`. Provider-executed tool calls skip local
execution. `StreamPartTypeToolResult` with `ProviderExecuted: true` is
accumulated inline (matching fantasy's own agent.go pattern) instead of
post-stream synthesis.
- `coderd/chatd/chatprompt/` — `MarshalToolResult` carries
`ProviderMetadata` through DB persistence so multi-turn round-trips work
(Anthropic needs `encrypted_content` back)
## Frontend
- Source citations render **inline** at the tool-call position (not
bottom-of-message), using `ToolCollapsible` so they look like other tool
cards — collapsed "Searched N results" with globe icon, expand to see
source pills
- Provider-executed tool calls/results are hidden from the normal tool
card UI
- Tool-role messages with only provider-executed results return `null`
(no empty bubble)
- Both persisted (messageParsing.ts) and streaming (streamState.ts)
paths group consecutive `source` parts into a single `{ type: "sources"
}` render block
## Fantasy changes
The fantasy fork (`kylecarbs/fantasy` branch `cj/go1.25`) has the
Anthropic tool code merged in, but will hopefully go upstream from:
https://github.com/charmbracelet/fantasy/pull/163
Adds `pull_request_title` and `pull_request_draft` to the chat diff
status pipeline (DB → provider → SDK → frontend). The GitHub provider
now fetches the PR title alongside existing status fields.
The agents sidebar now displays PR-state-aware icons for chats that have
a linked pull request (when the chat is in waiting/completed state):
- **Open PR**: `GitPullRequestArrow` (green)
- **Draft PR**: `GitPullRequestDraft` (gray)
- **Merged PR**: `GitMerge` (purple)
- **Closed PR**: `GitPullRequestClosed` (red)
Running/pending/paused/error chats keep their existing activity icons
(spinner, pause, error triangle).
### Changes
**Database migration** (`000432`): Adds `pull_request_title TEXT` and
`pull_request_draft BOOLEAN` columns to `chat_diff_statuses`.
**Backend pipeline**:
- `gitprovider.PRStatus` gains a `Title` field
- GitHub provider decodes the `title` from the API response
- `gitsync` and `coderd/chats.go` pass title + draft through to the DB
upsert
- `codersdk.ChatDiffStatus` exposes both new fields in the API response
**Frontend** (`AgentsSidebar.tsx`): New `getPRIconConfig()` function
resolves the appropriate Lucide git icon based on `pull_request_state`
and `pull_request_draft`. Only applies when the chat is in a terminal
state (waiting/completed).
**Real-time sync**: No changes needed — the existing
`diff_status_change` pubsub event already propagates the full
`ChatDiffStatus` including the new fields.
Replace the standalone `?archived=` query parameter on the chats listing
endpoint with a `?q=` search parameter, consistent with how workspaces,
tasks, templates, and other list endpoints work.
The `q` parameter uses the standard `key:value` search syntax parsed by
the `searchquery` package. Currently supports:
- `archived:true/false` (default: `false`, hides archived chats)
When `q` is empty or omits the archived filter, archived chats are
excluded by default. This is a behavioral change — the previous API
returned all chats (including archived) when no filter was specified.
### Changes
**Backend:**
- Add `searchquery.Chats()` parser following the same pattern as
`Tasks()`, `Workspaces()`, etc.
- Update `listChats` handler to read `q` instead of `archived`
- Update `codersdk.ListChatsOptions` to use `Q string` instead of
`Archived *bool`
**Frontend:**
- Update `getChats` API method to accept `q` parameter
- Update `infiniteChats` query to pass `q` instead of `archived`
**Tests:**
- Add `TestSearchChats` unit tests for the parser
- Update existing archive/unarchive integration tests to use `Q:
"archived:true"` syntax
Adds a `created_by` column (nullable UUID) to the `chat_messages` table
to track which user created each message. Only user-sent messages
populate this field; assistant, tool, system, and summary messages leave
it null.
The column is threaded through the full stack: SQL migration, query
updates, generated Go/TypeScript types, db2sdk conversion, chatd
(including subagent paths), and API handlers. All API handlers that
insert user messages now pass the authenticated user's ID as
`created_by`.
No foreign key constraint was added, matching the existing pattern used
by `chat_model_configs.created_by`.
Adds a user-level custom prompt to the database.
I'll be doing a follow-up for the UI, as we currently do not have
user-level settings (it's just admin). I'll also make it very obvious
for chats where there is a user-level prompt, but I don't know how yet.
Adds offset and cursor-based pagination to the `GET
/api/experimental/chats` endpoint, following the exact same patterns
used by `GetUsers` and `GetTemplateVersionsByTemplateID`.
## Changes
### Database
- Add `after_id`, `offset_opt`, `limit_opt` params to
`GetChatsByOwnerID` SQL query
- Use composite `(updated_at, id) DESC` cursor for stable, deterministic
pagination
- Add migration with composite index on `chats (owner_id, updated_at
DESC, id DESC)`
### Backend
- Use `ParsePagination()` in `listChats` handler (matches `users.go`
pattern)
- Add `Pagination` field to `ListChatsOptions` SDK struct
### Frontend
- Add `infiniteChats()` query factory using `useInfiniteQuery` with
offset-based page params (same pattern as `infiniteWorkspaceBuilds`)
- Update `AgentsPage` to use `useInfiniteQuery`
- Add "Show more" button at the bottom of the agents sidebar (matches
`HistorySidebar` pattern)
- Keep existing `chats()` query for non-paginated uses (e.g., parent
chat lookup in `AgentDetail`)
### Tests
- Add `TestListChats/Pagination` covering `limit`, `after_id` cursor,
`offset`, and no-limit behavior
## Problem
The Admin → Agents → System Prompt textarea saved only to the browser's
`localStorage`. The value was never sent to the backend, never stored in
the database, and never injected into chats. Entering text, clicking
Save, and refreshing the page showed no changes — the prompt was
effectively a no-op.
## Root Cause
Three disconnected layers:
1. **Frontend** wrote to `localStorage`, never called an API.
2. **`handleCreateChat`** never read `savedSystemPrompt`.
3. **Backend** hardcoded `chatd.DefaultSystemPrompt` on every chat
creation — no field in `CreateChatRequest` accepted a custom prompt.
## Changes
### Database
- Added `GetChatSystemPrompt` / `UpsertChatSystemPrompt` queries on the
existing `site_configs` table (no migration needed).
### API
- `GET /api/experimental/chats/system-prompt` — returns the configured
prompt (any authenticated user).
- `PUT /api/experimental/chats/system-prompt` — sets the prompt
(admin-only, `rbac: deployment_config update`).
- Input validation: max 32 KiB prompt length.
### Backend
- `resolvedChatSystemPrompt(ctx)` checks for a custom prompt in the DB,
falls back to `chatd.DefaultSystemPrompt` when empty/unset.
- Logs a warning on DB errors instead of silently swallowing them.
- Replaced the hardcoded `defaultChatSystemPrompt()` call in chat
creation.
### Frontend
- Replaced `localStorage` read/write with React Query
`useQuery`/`useMutation` backed by the new endpoints.
- Fixed `useEffect` draft sync to avoid clobbering in-progress user
edits on refetch.
- Added `try/catch` error handling on save (draft stays dirty for
retry).
- Save button disabled during mutation (`isSavingSystemPrompt`).
- Query key follows kebab-case convention (`chat-system-prompt`).
### UX
- Added hint: "When empty, the built-in default prompt is used."
### Tests
- `TestChatSystemPrompt`: GET returns empty when unset, admin can set,
non-admin gets 403.
- dbauthz `TestMethodTestSuite` coverage for both new querier methods.
## Summary
Adds a line-reference and annotation system for diffs in the Agents UI.
Users can click line numbers in the Git diff panel to open an inline
prompt input, type a comment, and have a reference chip + text added to
the chat message input.
## Changes
### Backend
- Added `diff-comment` type to `ChatInputPart` and `ChatMessagePart` in
`codersdk/chats.go` with `FileName`, `StartLine`, `EndLine`, `Side`
fields
### Frontend
- **`DiffCommentContext`**: React context/provider managing pending diff
comments with `addReference`, `removeComment`, `restoreComment`,
`clearComments`
- **`DiffCommentNode`**: Lexical `DecoratorNode` rendering inline chips
in the chat input showing file:line references. Chips are clickable
(scroll to line in diff), removable, and support undo/redo via mutation
tracking
- **`InlinePromptInput`**: Textarea annotation rendered inline under
clicked lines in the diff. Supports multiline (Shift+Enter), submit
(Enter), cancel (Escape)
- **`FilesChangedPanel`**: Line click/drag-select handlers open the
inline input. On submit, a badge chip + plain text are inserted into the
Lexical editor
- **`AgentDetail`**: Bidirectional sync between DiffCommentContext and
Lexical editor. Comments are sent as `diff-comment` parts on message
submit
- **`ConversationTimeline`**: Renders `diff-comment` message parts with
file:line labels
## How it works
1. Click a line number in the diff → inline textarea appears below that
line
2. Type a comment and press Enter → reference chip appears in chat input
with your text after it
3. Send the message → diff-comment parts are included alongside the
message text
This change adds support for image attachments to chat via add button
and clipboard paste. Files are stored in a new `chat_files` table and
referenced by ID in message content. File data is resolved from storage
at LLM dispatch time, keeping the message content column small.
Upload validates MIME types via content type or content sniffing against
an allowlist (png, jpeg, gif, webp). The retrieval endpoint serves files
with immutable caching headers. On the frontend, uploads start eagerly
on attach with a background fetch to pre-warm the browser HTTP cache so
the timeline renders instantly after send.
## Summary
Fixes a bug where interrupting a streaming chat and sending a new
message
left the relay connected to the wrong replica. Expanded into a broader
refactor that cleanly separates concerns:
- **OSS** owns pubsub subscription, message catch-up, queue updates,
status forwarding, and local parts merging.
- **Enterprise** (`enterprise/coderd/chatd`) only manages relay dialing,
reconnection, and stale-dial discarding for cross-replica streaming.
## Architecture
### OSS `coderd/chatd/chatd.go`
`Subscribe()` builds the initial snapshot then runs a single merge
goroutine that handles:
- Pubsub subscription for durable events (status, messages, queue,
errors)
- Message catch-up via `AfterMessageID`
- Local `message_part` forwarding
- Relay events from enterprise (when `SubscribeFn` is set)
- Sends `StatusNotification` to enterprise so it can manage relay
lifecycle
Key types:
- `SubscribeFn` — enterprise hook, returns relay-only events channel
- `SubscribeFnParams` — `ChatID`, `Chat`, `WorkerID`,
`StatusNotifications`, `RequestHeader`, `DB`, `Logger`
- `StatusNotification` — `Status` + `WorkerID`, sent to enterprise on
pubsub status changes
### Enterprise `enterprise/coderd/chatd/chatd.go`
`NewMultiReplicaSubscribeFn(cfg MultiReplicaSubscribeConfig)` returns a
`SubscribeFn` that:
- Opens an initial synchronous relay if the chat is running on a remote
worker
- Reads `StatusNotifications` from OSS to open/close relay connections
- Handles async dial, reconnect timers, stale-dial discarding
- Returns only relay `message_part` events
## Bug fixes
### Original bug: stale relay dial after interrupt
`openRelayAsync` goroutines used `mergedCtx` (subscription-level), not a
per-dial context. `closeRelay()` could not cancel in-flight dials. When
the user interrupts and a new replica picks up the chat, the old dial
goroutine could complete after the new one and deliver a stale
`relayResult`.
**Fix**: per-dial `dialCtx`/`dialCancel`, `expectedWorkerID` tracking,
`workerID` on `relayResult`. `closeRelay()` cancels the dial context and
drains `relayReadyCh`. Merge loop rejects mismatched worker IDs.
### Additional fixes
- `statusNotifications` send-on-closed-channel race — goroutine now owns
`close()` via defer
- Enterprise spin-loop on `StatusNotifications` close — two-value
receive
with nil-out
- `hasPubsub` set from `p.pubsub != nil` instead of subscription success
— now tracks actual subscription result
- `lastMessageID` not initialized from `afterMessageID` — caused
duplicate messages on catch-up
- `wrappedParts` goroutine leaked remote connection on `dialCtx` cancel
- `closeRelay()` did not drain `relayReadyCh`
- `setChatWaiting` race with `SendMessage(Interrupt)` — wrapped in
`InTx`
- `processChat` post-TX side effects fired when chat was taken by
another
worker — added `errChatTakenByOtherWorker` sentinel
- Cancel closure data race on `reconnectTimer`
- Bare blocking send on pubsub error path
- `localParts` hot-spin after channel close
- No-pubsub branch dropped relay events and initial snapshot
- Failed relay dial caused permanent stall (no reconnect retry)
- DB error during reconnect timer caused permanent stall
- `time.NewTimer` replaced with `quartz.Clock` for testable timing
## Tests
9 enterprise tests covering:
- Relay reconnect on drop (mock clock)
- Async dial does not block merge loop
- Relay snapshot delivery
- Stale dial discarded after interrupt
- Cancel during in-flight dial
- Running-to-running worker switch
- Failed dial retries (mock clock)
- Local worker closes relay
- Multiple consecutive reconnects (mock clock)
All pass with `-race`.
Despite the SDK type having an `Archived` field for chats, this data was
never fetched from the database — the `GetChatsByOwnerID` query
hardcoded `AND archived = false`, and the `convertChat` function never
mapped the field.
This PR adds an optional `archived` query parameter to `GET
/api/experimental/chats`:
| Value | Behavior |
|-------|----------|
| *(not provided)* | Returns all chats (active and archived) |
| `archived=false` | Returns only non-archived chats |
| `archived=true` | Returns only archived chats |
This follows the same pattern used by template versions
(`sqlc.narg('archived')` nullable boolean).
Also fixes `convertChat` to populate the `Archived` field in API
responses, which was never being set despite existing on the SDK type.
## Summary
Remove the `workspace_agent_id` column from the `chats` table and
dynamically look up the first workspace agent instead.
## Problem
When a workspace is stopped and restarted, the workspace agent gets a
new ID. The `workspace_agent_id` stored on the chat at creation time
becomes stale, making the agent unreachable. This caused chats to break
after workspace restarts.
## Solution
Instead of persisting the agent ID, dynamically look up the first agent
from the workspace's latest build via
`GetWorkspaceAgentsInLatestBuildByWorkspaceID` whenever an agent
connection is needed. The `workspace_id` on the chat remains stable
across restarts.
This behavior may be refined later (e.g., agent selection heuristics),
but picking the first agent resolves the immediate breakage.
## Changes
- **Migration 000425**: Drop `workspace_agent_id` column from `chats`
- **SQL queries**: Remove `workspace_agent_id` from `InsertChat` and
`UpdateChatWorkspace`
- **chatd.go**: `getWorkspaceConn` and `resolveInstructions` now look up
agents dynamically from workspace ID
- **chatd.go**: Remove `refreshChatWorkspaceSnapshot` (no longer needed)
- **createworkspace.go**: Stop persisting agent ID when associating
workspace with chat
- **subagent.go**: Stop passing agent ID to child chats
- **SDK/frontend**: Remove `WorkspaceAgentID` / `workspace_agent_id`
from Chat type
---------
Co-authored-by: Kyle Carberry <kylecarbs@gmail.com>
Adds a nullable `last_error` column to the `chats` table so error
reasons survive page reloads.
**Backend:**
- Migration adds `last_error TEXT` (nullable) to chats
- `UpdateChatStatus` writes the error reason when status transitions to
`error`, clears it (NULL) on recovery
- `convertChat` maps `sql.NullString` to `*string` in the SDK
**Frontend:**
- Sidebar falls back to `chat.last_error` when no stream error reason is
cached
- Chat detail page does the same for `persistedErrorReason`
- Fixtures updated for new required field
## Summary
The UI has always labeled the action as "Archive agent" but the backend
was performing a hard `DELETE`, permanently destroying chats and all
their messages.
This change replaces the hard delete with a soft archive, consistent
with the pattern used by template versions.
## Changes
### Database
- **Migration 000423**: Add `archived boolean DEFAULT false NOT NULL`
column to `chats` table
- Replace `DeleteChatByID` query with `ArchiveChatByID` (`UPDATE SET
archived = true`)
- Add `UnarchiveChatByID` query (`UPDATE SET archived = false`)
- Filter archived chats from `GetChatsByOwnerID` (`WHERE archived =
false`)
### API
- Remove `DELETE /api/experimental/chats/{chat}`
- Add `POST /api/experimental/chats/{chat}/archive` — archives a chat
and all its descendants
- Add `POST /api/experimental/chats/{chat}/unarchive` — unarchives a
single chat (API only, no UI yet)
### Backend
- `archiveChatTree()` recursively archives child chats (replaces
`deleteChatTree()` which hard-deleted)
- Chat daemon's `ArchiveChat()` archives the full chat tree in a
transaction
- Authorization uses `ActionUpdate` instead of `ActionDelete`
### SDK
- Replace `DeleteChat()` with `ArchiveChat()` and `UnarchiveChat()`
- Add `Archived` field to `Chat` struct
### Frontend
- `archiveChat` API call uses `POST .../archive` instead of `DELETE`
- No UI changes — the "Archive agent" button now actually archives
instead of deleting
## Design Decision
This follows the **template version archive pattern** (Pattern B in the
codebase):
- `archived boolean` column (not `deleted boolean`)
- Dedicated `POST .../archive` and `POST .../unarchive` routes (not
repurposing `DELETE`)
- Reversible — users can unarchive via the API (UI for this will come
later)
Kyle Carberry