feat(coderd/chatd): unify chat storage on SDK parts and fix file-reference rendering (#22958)

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

coderd/chatd/chatloop/chatloop.go

@@ -71,7 +71,7 @@ type RunOptions struct {
 
 	PersistStep        func(context.Context, PersistedStep) error
 	PublishMessagePart func(
-		role fantasy.MessageRole,
+		role codersdk.ChatMessageRole,
 		part codersdk.ChatMessagePart,
 	)
 	Compaction     *CompactionOptions
@@ -216,7 +216,7 @@ func Run(ctx context.Context, opts RunOptions) error {
 		opts.MaxSteps = 1
 	}
 
-	publishMessagePart := func(role fantasy.MessageRole, part codersdk.ChatMessagePart) {
+	publishMessagePart := func(role codersdk.ChatMessageRole, part codersdk.ChatMessagePart) {
 		if opts.PublishMessagePart == nil {
 			return
 		}
@@ -317,7 +317,7 @@ func Run(ctx context.Context, opts RunOptions) error {
 
 				toolResults = executeTools(ctx, opts.Tools, result.toolCalls, func(tr fantasy.ToolResultContent) {
 					publishMessagePart(
-						fantasy.MessageRoleTool,
+						codersdk.ChatMessageRoleTool,
 						chatprompt.PartFromContent(tr),
 					)
 				})
@@ -455,7 +455,7 @@ func Run(ctx context.Context, opts RunOptions) error {
 func processStepStream(
 	ctx context.Context,
 	stream fantasy.StreamResponse,
-	publishMessagePart func(fantasy.MessageRole, codersdk.ChatMessagePart),
+	publishMessagePart func(codersdk.ChatMessageRole, codersdk.ChatMessagePart),
 ) (stepResult, error) {
 	var result stepResult
 
@@ -474,10 +474,7 @@ func processStepStream(
 			if _, exists := activeTextContent[part.ID]; exists {
 				activeTextContent[part.ID] += part.Delta
 			}
-			publishMessagePart(fantasy.MessageRoleAssistant, codersdk.ChatMessagePart{
-				Type: codersdk.ChatMessagePartTypeText,
-				Text: part.Delta,
-			})
+			publishMessagePart(codersdk.ChatMessageRoleAssistant, codersdk.ChatMessageText(part.Delta))
 
 		case fantasy.StreamPartTypeTextEnd:
 			if text, exists := activeTextContent[part.ID]; exists {
@@ -500,10 +497,7 @@ func processStepStream(
 				active.options = part.ProviderMetadata
 				activeReasoningContent[part.ID] = active
 			}
-			publishMessagePart(fantasy.MessageRoleAssistant, codersdk.ChatMessagePart{
-				Type: codersdk.ChatMessagePartTypeReasoning,
-				Text: part.Delta,
-			})
+			publishMessagePart(codersdk.ChatMessageRoleAssistant, codersdk.ChatMessageReasoning(part.Delta))
 
 		case fantasy.StreamPartTypeReasoningEnd:
 			if active, exists := activeReasoningContent[part.ID]; exists {
@@ -535,7 +529,7 @@ func processStepStream(
 				providerExecuted = toolCall.ProviderExecuted
 			}
 			toolName := toolNames[part.ID]
-			publishMessagePart(fantasy.MessageRoleAssistant, codersdk.ChatMessagePart{
+			publishMessagePart(codersdk.ChatMessageRoleAssistant, codersdk.ChatMessagePart{
 				Type:             codersdk.ChatMessagePartTypeToolCall,
 				ToolCallID:       part.ID,
 				ToolName:         toolName,
@@ -563,7 +557,7 @@ func processStepStream(
 			delete(activeToolCalls, part.ID)
 
 			publishMessagePart(
-				fantasy.MessageRoleAssistant,
+				codersdk.ChatMessageRoleAssistant,
 				chatprompt.PartFromContent(tc),
 			)
 
@@ -577,7 +571,7 @@ func processStepStream(
 			}
 			result.content = append(result.content, sourceContent)
 			publishMessagePart(
-				fantasy.MessageRoleAssistant,
+				codersdk.ChatMessageRoleAssistant,
 				chatprompt.PartFromContent(sourceContent),
 			)
 
@@ -595,7 +589,7 @@ func processStepStream(
 				}
 				result.content = append(result.content, tr)
 				publishMessagePart(
-					fantasy.MessageRoleTool,
+					codersdk.ChatMessageRoleTool,
 					chatprompt.PartFromContent(tr),
 				)
 			}

coderd/chatd/chatloop/compaction.go

@@ -55,7 +55,7 @@ type CompactionOptions struct {
 	// PublishMessagePart publishes streaming parts to connected
 	// clients so they see "Summarizing..." / "Summarized" UI
 	// transitions during compaction.
-	PublishMessagePart func(fantasy.MessageRole, codersdk.ChatMessagePart)
+	PublishMessagePart func(codersdk.ChatMessageRole, codersdk.ChatMessagePart)
 
 	OnError func(error)
 }
@@ -110,12 +110,8 @@ func tryCompact(
 	// connected clients see activity during summary generation.
 	if config.PublishMessagePart != nil && config.ToolCallID != "" {
 		config.PublishMessagePart(
-			fantasy.MessageRoleAssistant,
-			codersdk.ChatMessagePart{
-				Type:       codersdk.ChatMessagePartTypeToolCall,
-				ToolCallID: config.ToolCallID,
-				ToolName:   config.ToolName,
-			},
+			codersdk.ChatMessageRoleAssistant,
+			codersdk.ChatMessageToolCall(config.ToolCallID, config.ToolName, nil),
 		)
 	}
 
@@ -163,13 +159,8 @@ func tryCompact(
 			"context_limit_tokens": contextLimit,
 		})
 		config.PublishMessagePart(
-			fantasy.MessageRoleTool,
-			codersdk.ChatMessagePart{
-				Type:       codersdk.ChatMessagePartTypeToolResult,
-				ToolCallID: config.ToolCallID,
-				ToolName:   config.ToolName,
-				Result:     resultJSON,
-			},
+			codersdk.ChatMessageRoleTool,
+			codersdk.ChatMessageToolResult(config.ToolCallID, config.ToolName, resultJSON, false),
 		)
 	}
 
@@ -186,14 +177,8 @@ func publishCompactionError(config CompactionOptions, msg string) {
 		"error": msg,
 	})
 	config.PublishMessagePart(
-		fantasy.MessageRoleTool,
-		codersdk.ChatMessagePart{
-			Type:       codersdk.ChatMessagePartTypeToolResult,
-			ToolCallID: config.ToolCallID,
-			ToolName:   config.ToolName,
-			Result:     errJSON,
-			IsError:    true,
-		},
+		codersdk.ChatMessageRoleTool,
+		codersdk.ChatMessageToolResult(config.ToolCallID, config.ToolName, errJSON, true),
 	)
 }
 

coderd/chatd/chatloop/compaction_test.go

@@ -149,7 +149,7 @@ func TestRun_Compaction(t *testing.T) {
 				SummaryPrompt:    "summarize now",
 				ToolCallID:       "test-tool-call-id",
 				ToolName:         "chat_summarized",
-				PublishMessagePart: func(role fantasy.MessageRole, part codersdk.ChatMessagePart) {
+				PublishMessagePart: func(role codersdk.ChatMessageRole, part codersdk.ChatMessagePart) {
 					switch part.Type {
 					case codersdk.ChatMessagePartTypeToolCall:
 						callOrder = append(callOrder, "publish_tool_call")
@@ -218,7 +218,7 @@ func TestRun_Compaction(t *testing.T) {
 				ThresholdPercent: 70,
 				ToolCallID:       "test-tool-call-id",
 				ToolName:         "chat_summarized",
-				PublishMessagePart: func(_ fantasy.MessageRole, _ codersdk.ChatMessagePart) {
+				PublishMessagePart: func(_ codersdk.ChatMessageRole, _ codersdk.ChatMessagePart) {
 					publishCalled = true
 				},
 				Persist: func(_ context.Context, _ CompactionResult) error {