fix(todo-continuation): normalize agent name to config key before promptAsync (#3149)

The todo-continuation-enforcer was passing raw agent names (which could be
display names like 'Sisyphus (Ultraworker)') to promptAsync. These names
contain spaces/parentheses that violate HTTP header specs, causing the
x-opencode-agent-name header validation to fail with 'unknown error' toast.

Added normalizeAgentForPromptKey() that converts display names to config keys
(e.g., 'Sisyphus (Ultraworker)' -> 'sisyphus') before API calls.

TDD: Added regression test that verifies config key is sent to promptAsync.

src/shared/agent-display-names.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "bun:test"
-import { AGENT_DISPLAY_NAMES, getAgentConfigKey, getAgentDisplayName, getAgentListDisplayName, normalizeAgentForPrompt } from "./agent-display-names"
+import { AGENT_DISPLAY_NAMES, getAgentConfigKey, getAgentDisplayName, getAgentListDisplayName, normalizeAgentForPrompt, normalizeAgentForPromptKey } from "./agent-display-names"
 
 describe("getAgentDisplayName", () => {
   it("returns display name for lowercase config key (new format)", () => {
@@ -196,6 +196,16 @@ describe("normalizeAgentForPrompt", () => {
   })
 })
 
+describe("normalizeAgentForPromptKey", () => {
+  it("converts built-in display names to config keys", () => {
+    expect(normalizeAgentForPromptKey("Sisyphus (Ultraworker)")).toBe("sisyphus")
+  })
+
+  it("preserves custom agents", () => {
+    expect(normalizeAgentForPromptKey("MyCustomAgent")).toBe("MyCustomAgent")
+  })
+})
+
 describe("AGENT_DISPLAY_NAMES", () => {
   it("contains all expected agent mappings", () => {
     // given expected mappings

src/shared/agent-display-names.ts

@@ -98,3 +98,25 @@ export function normalizeAgentForPrompt(agentName: string | undefined): string |
 
   return trimmed
 }
+
+export function normalizeAgentForPromptKey(agentName: string | undefined): string | undefined {
+  if (typeof agentName !== "string") {
+    return undefined
+  }
+
+  const trimmed = stripAgentListSortPrefix(agentName.trim())
+  if (!trimmed) {
+    return undefined
+  }
+
+  const lower = trimmed.toLowerCase()
+  const reversed = REVERSE_DISPLAY_NAMES[lower]
+  if (reversed !== undefined) {
+    return reversed
+  }
+  if (AGENT_DISPLAY_NAMES[lower] !== undefined) {
+    return lower
+  }
+
+  return trimmed
+}