coder · ibetitsmike · Aug 18, 2026 · Jul 29, 2026 · Jul 30, 2026 · Jul 30, 2026
diff --git a/coderd/apidoc/docs.go b/coderd/apidoc/docs.go
diff --git a/coderd/apidoc/swagger.json b/coderd/apidoc/swagger.json
diff --git a/coderd/audit/audit.go b/coderd/audit/audit.go
@@ -42,9 +42,19 @@ func NewMock() *MockAuditor {
 	return &MockAuditor{}
 }
 
+// NewMockWithDiffFn returns a MockAuditor whose entries carry diffs computed
+// by the supplied function instead of the default empty diff. Tests use it to
+// pin the Old/New pair a handler captured, which the empty diff cannot
+// express. The function is test-supplied comparison logic; the mock never
+// calls the production differ.
+func NewMockWithDiffFn(fn func(old, newVal any) Map) *MockAuditor {
+	return &MockAuditor{diffFn: fn}
+}
+
 type MockAuditor struct {
 	mutex     sync.Mutex
 	auditLogs []database.AuditLog
+	diffFn    func(old, newVal any) Map
 }
 
 // ResetLogs removes all audit logs from the mock auditor.
@@ -70,8 +80,13 @@ func (a *MockAuditor) Export(_ context.Context, alog database.AuditLog) error {
 	return nil
 }
 
-func (*MockAuditor) diff(any, any) Map {
-	return Map{}
+func (a *MockAuditor) diff(old, newVal any) Map {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	if a.diffFn == nil {
+		return Map{}
+	}
+	return a.diffFn(old, newVal)
 }
 
 // Contains returns true if, for each non-zero-valued field in expected,

diff --git a/coderd/audit/diff.go b/coderd/audit/diff.go
@@ -42,7 +42,8 @@ type Auditable interface {
 		database.AuditableGroupAIBudget |
 		database.AuditableUserAIBudgetOverride |
 		database.UserSecret |
-		database.UserSkill
+		database.UserSkill |
+		database.ChatInstructionSettings
 }
 
 // Map is a map of changed fields in an audited resource. It maps field names to

diff --git a/coderd/audit/request.go b/coderd/audit/request.go
@@ -158,6 +158,8 @@ func ResourceTarget[T Auditable](tgt T) string {
 		return typed.Name
 	case database.UserSkill:
 		return typed.Name
+	case database.ChatInstructionSettings:
+		return typed.Name
 	default:
 		panic(fmt.Sprintf("unknown resource %T for ResourceTarget", tgt))
 	}
@@ -168,6 +170,22 @@ func ResourceTarget[T Auditable](tgt T) string {
 // 51A51C = "Static"
 var noID = uuid.MustParse("51A51C00-0000-0000-0000-000000000000")
 
+// Fixed IDs for the two chat instruction settings. History-by-setting works
+// only if every change to one setting carries the same resource ID, so
+// unlike the per-write artificial IDs of the other settings singletons,
+// these never change. C1A7 = "Chat".
+var (
+	ChatInstructionSystemPromptID = uuid.MustParse("C1A715C0-0000-0000-0000-000000000001")
+	ChatInstructionPlanModeID     = uuid.MustParse("C1A715C0-0000-0000-0000-000000000002")
+)
+
+// Human-readable targets for the two chat instruction settings, so an audit
+// row names the setting it concerns.
+const (
+	ChatInstructionSystemPromptName = "System prompt"
+	ChatInstructionPlanModeName     = "Plan mode instructions"
+)
+
 func ResourceID[T Auditable](tgt T) uuid.UUID {
 	switch typed := any(tgt).(type) {
 	case database.Template:
@@ -243,6 +261,9 @@ func ResourceID[T Auditable](tgt T) uuid.UUID {
 		return typed.ID
 	case database.UserSkill:
 		return typed.ID
+	case database.ChatInstructionSettings:
+		// Fixed ID per setting; see ChatInstructionSettings IDs.
+		return typed.ID
 	default:
 		panic(fmt.Sprintf("unknown resource %T for ResourceID", tgt))
 	}
@@ -318,6 +339,8 @@ func ResourceType[T Auditable](tgt T) database.ResourceType {
 		return database.ResourceTypeUserSecret
 	case database.UserSkill:
 		return database.ResourceTypeUserSkill
+	case database.ChatInstructionSettings:
+		return database.ResourceTypeChatInstructionSettings
 	default:
 		panic(fmt.Sprintf("unknown resource %T for ResourceType", typed))
 	}
@@ -408,6 +431,9 @@ func ResourceRequiresOrgID[T Auditable]() bool {
 	case database.UserSkill:
 		// User skills are global to the user across organizations.
 		return false
+	case database.ChatInstructionSettings:
+		// Deployment settings, not scoped to any organization.
+		return false
 	default:
 		panic(fmt.Sprintf("unknown resource %T for ResourceRequiresOrgID", tgt))
 	}

diff --git a/coderd/database/dump.sql b/coderd/database/dump.sql
diff --git a/coderd/database/lock.go b/coderd/database/lock.go
@@ -20,6 +20,17 @@ const (
 	LockIDChatCapacityAdmission
 )
 
+// Per-setting advisory lock IDs for the chat instruction settings. These
+// derive from the exact site_configs key with GenLockID (FNV-1a 64) instead
+// of the sequential LockID* block above, so writers of different settings
+// never contend and the IDs cannot collide with any sequentially allocated
+// lock ID (different derivation space) or with another subsystem's
+// GenLockID output (the key strings are unique to these settings).
+var (
+	LockIDChatInstructionSystemPrompt = GenLockID("agents_chat_system_prompt")
+	LockIDChatInstructionPlanMode     = GenLockID("agents_chat_plan_mode_instructions")
+)
+
 // GenLockID generates a unique and consistent lock ID from a given string.
 func GenLockID(name string) int64 {
 	hash := fnv.New64()

diff --git a/coderd/database/lock_internal_test.go b/coderd/database/lock_internal_test.go
@@ -0,0 +1,50 @@
+package database
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestChatInstructionLockIDsDistinct proves the per-setting advisory lock IDs
+// for the chat instruction settings cannot collide with each other or with
+// any sequentially allocated LockID* constant. The constants are listed
+// explicitly rather than enumerated programmatically (there is no registry of
+// iota constants), so a future LockID* addition that collides fails here in
+// review, not in a production deadlock.
+func TestChatInstructionLockIDsDistinct(t *testing.T) {
+	t.Parallel()
+
+	generated := map[string]int64{
+		"LockIDChatInstructionSystemPrompt": LockIDChatInstructionSystemPrompt,
+		"LockIDChatInstructionPlanMode":     LockIDChatInstructionPlanMode,
+	}
+
+	sequential := map[string]int64{
+		"LockIDDeploymentSetup":              LockIDDeploymentSetup,
+		"LockIDEnterpriseDeploymentSetup":    LockIDEnterpriseDeploymentSetup,
+		"LockIDDBRollup":                     LockIDDBRollup,
+		"LockIDDBPurge":                      LockIDDBPurge,
+		"LockIDNotificationsReportGenerator": LockIDNotificationsReportGenerator,
+		"LockIDCryptoKeyRotation":            LockIDCryptoKeyRotation,
+		"LockIDReconcilePrebuilds":           LockIDReconcilePrebuilds,
+		"LockIDReconcileSystemRoles":         LockIDReconcileSystemRoles,
+		"LockIDBoundaryUsageStats":           LockIDBoundaryUsageStats,
+		"LockIDAIProvidersEnvSeed":           LockIDAIProvidersEnvSeed,
+		"LockIDChatModelConfigWrites":        LockIDChatModelConfigWrites,
+	}
+
+	// The two generated IDs are pairwise distinct.
+	require.NotEqual(t,
+		LockIDChatInstructionSystemPrompt,
+		LockIDChatInstructionPlanMode,
+		"per-setting lock IDs must differ from each other")
+
+	// Neither generated ID collides with any sequential constant.
+	for name, id := range generated {
+		for seqName, seqID := range sequential {
+			require.NotEqualf(t, seqID, id,
+				"%s (%d) collides with sequential constant %s", name, id, seqName)
+		}
+	}
+}
diff --git a/coderd/database/migrations/000573_audit_chat_instruction_settings.down.sql b/coderd/database/migrations/000573_audit_chat_instruction_settings.down.sql
@@ -0,0 +1 @@
+-- No-op, enum values can't be dropped.
diff --git a/coderd/database/migrations/000573_audit_chat_instruction_settings.up.sql b/coderd/database/migrations/000573_audit_chat_instruction_settings.up.sql
@@ -0,0 +1,2 @@
+ALTER TYPE resource_type
+	ADD VALUE IF NOT EXISTS 'chat_instruction_settings';
diff --git a/coderd/database/models.go b/coderd/database/models.go
diff --git a/coderd/database/queries.sql.go b/coderd/database/queries.sql.go
diff --git a/coderd/database/queries/siteconfig.sql b/coderd/database/queries/siteconfig.sql
@@ -175,7 +175,12 @@ SELECT
             WHERE key = 'agents_chat_system_prompt'
                 AND value != ''
         )
-    ) :: boolean AS include_default_system_prompt;
+    ) :: boolean AS include_default_system_prompt,
+    EXISTS (
+        SELECT 1
+        FROM site_configs
+        WHERE key = 'agents_chat_include_default_system_prompt'
+    ) :: boolean AS include_default_system_prompt_set;
 
 -- name: UpsertChatSystemPrompt :exec
 INSERT INTO site_configs (key, value) VALUES ('agents_chat_system_prompt', $1)

diff --git a/coderd/database/types.go b/coderd/database/types.go
@@ -49,6 +49,27 @@ type OAuth2ProviderSettings struct {
 	DynamicClientRegistrationEnabled bool      `db:"dynamic_client_registration_enabled" json:"dynamic_client_registration_enabled"`
 }
 
+// ChatInstructionSettings is the auditable shape of the deployment-wide
+// chat instruction configuration, stored across the
+// agents_chat_system_prompt, agents_chat_include_default_system_prompt and
+// agents_chat_plan_mode_instructions site_configs keys. Both the
+// system-prompt and plan-mode-instructions endpoints audit this one type;
+// each populates only the fields its endpoint can change.
+type ChatInstructionSettings struct {
+	ID uuid.UUID `db:"id" json:"id"`
+	// Name identifies which setting an audit row concerns (e.g. "System
+	// prompt"). It is ignored in diffs and set identically on Old and New.
+	Name         string `db:"name" json:"name"`
+	SystemPrompt string `db:"system_prompt" json:"system_prompt"`
+	// IncludeDefaultSystemPromptSet records whether the override row
+	// exists, not only its effective value: writing explicit false over a
+	// legacy absent row does not move the effective value but changes
+	// future behavior, so presence must enter the diff.
+	IncludeDefaultSystemPromptSet bool   `db:"include_default_system_prompt_set" json:"include_default_system_prompt_set"`
+	IncludeDefaultSystemPrompt    bool   `db:"include_default_system_prompt" json:"include_default_system_prompt"`
+	PlanModeInstructions          string `db:"plan_mode_instructions" json:"plan_mode_instructions"`
+}
+
 type Actions []policy.Action
 
 func (a *Actions) Scan(src interface{}) error {
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		ALTER TYPE resource_type
		ADD VALUE IF NOT EXISTS 'chat_instruction_settings';