diff --git a/src/shared/agent-runtime-name-sort.test.ts b/src/shared/agent-runtime-name-sort.test.ts
new file mode 100644
index 000000000..c39b4a545
--- /dev/null
+++ b/src/shared/agent-runtime-name-sort.test.ts
@@ -0,0 +1,152 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, it, test } from "bun:test"
+
+import {
+  AGENT_DISPLAY_NAMES,
+  getAgentRuntimeName,
+  normalizeAgentForPromptKey,
+} from "./agent-display-names"
+
+// OpenCode Agent.list() sorts via remeda sortBy: default_agent desc, then name asc localeCompare.
+// Reference: ../opencode/packages/opencode/src/agent/agent.ts:284-293.
+// Earlier ZWSP prefixes silently failed: Unicode collation treats zero-width chars as ignorable.
+function simulateOpencodeSort(agentNames: string[], defaultName: string): string[] {
+  return [...agentNames].sort((a, b) => {
+    const aIsDefault = a === defaultName ? 1 : 0
+    const bIsDefault = b === defaultName ? 1 : 0
+    if (aIsDefault !== bIsDefault) return bIsDefault - aIsDefault
+    return a.localeCompare(b)
+  })
+}
+
+describe("OpenCode Agent.list() sort with runtime-name prefixes", () => {
+  describe("#given the four core agents and a mix of non-core agents", () => {
+    test("#when sorted using opencode-style sortBy #then core agents come first in canonical order", () => {
+      const sisyphus = getAgentRuntimeName("sisyphus")
+      const hephaestus = getAgentRuntimeName("hephaestus")
+      const prometheus = getAgentRuntimeName("prometheus")
+      const atlas = getAgentRuntimeName("atlas")
+
+      const allAgents = [
+        sisyphus,
+        hephaestus,
+        prometheus,
+        atlas,
+        "athena",
+        "explore",
+        "metis",
+        "oracle",
+      ]
+
+      const sorted = simulateOpencodeSort(allAgents, sisyphus)
+      const orderedConfigKeys = sorted.map((name) => normalizeAgentForPromptKey(name))
+
+      expect(orderedConfigKeys).toEqual([
+        "sisyphus",
+        "hephaestus",
+        "prometheus",
+        "atlas",
+        "athena",
+        "explore",
+        "metis",
+        "oracle",
+      ])
+    })
+
+    test("#when default_agent is unset #then canonical core order still holds via prefix alone", () => {
+      const sisyphus = getAgentRuntimeName("sisyphus")
+      const hephaestus = getAgentRuntimeName("hephaestus")
+      const prometheus = getAgentRuntimeName("prometheus")
+      const atlas = getAgentRuntimeName("atlas")
+
+      const allAgents = [hephaestus, prometheus, atlas, sisyphus, "athena", "oracle"]
+
+      const sorted = simulateOpencodeSort(allAgents, "no-such-default-agent")
+      const orderedConfigKeys = sorted.map((name) => normalizeAgentForPromptKey(name))
+
+      expect(orderedConfigKeys.slice(0, 4)).toEqual([
+        "sisyphus",
+        "hephaestus",
+        "prometheus",
+        "atlas",
+      ])
+    })
+  })
+
+  describe("#given input array in random order", () => {
+    test("#when sorted with opencode comparator #then result is always canonical", () => {
+      const sisyphus = getAgentRuntimeName("sisyphus")
+      const hephaestus = getAgentRuntimeName("hephaestus")
+      const prometheus = getAgentRuntimeName("prometheus")
+      const atlas = getAgentRuntimeName("atlas")
+      const nonCore = ["athena", "explore", "librarian", "metis", "oracle"]
+      const allAgents = [...nonCore, atlas, prometheus, hephaestus, sisyphus]
+
+      for (let attempt = 0; attempt < 25; attempt += 1) {
+        const shuffled = [...allAgents]
+        for (let i = shuffled.length - 1; i > 0; i -= 1) {
+          const j = Math.floor(Math.random() * (i + 1))
+          ;[shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]]
+        }
+        const sorted = simulateOpencodeSort(shuffled, sisyphus)
+        const orderedConfigKeys = sorted.map((name) => normalizeAgentForPromptKey(name))
+
+        expect(orderedConfigKeys).toEqual([
+          "sisyphus",
+          "hephaestus",
+          "prometheus",
+          "atlas",
+          "athena",
+          "explore",
+          "librarian",
+          "metis",
+          "oracle",
+        ])
+      }
+    })
+  })
+
+  describe("#given runtime names containing only core agents", () => {
+    test("#when sorted #then sisyphus, hephaestus, prometheus, atlas in that order", () => {
+      const sisyphus = getAgentRuntimeName("sisyphus")
+      const hephaestus = getAgentRuntimeName("hephaestus")
+      const prometheus = getAgentRuntimeName("prometheus")
+      const atlas = getAgentRuntimeName("atlas")
+
+      const sorted = simulateOpencodeSort([atlas, prometheus, hephaestus, sisyphus], sisyphus)
+      const orderedConfigKeys = sorted.map((name) => normalizeAgentForPromptKey(name))
+
+      expect(orderedConfigKeys).toEqual([
+        "sisyphus",
+        "hephaestus",
+        "prometheus",
+        "atlas",
+      ])
+    })
+  })
+
+  describe("#given the prefix is meant to render in OpenCode TUI", () => {
+    it("uses ASCII whitespace so terminals render the prefix without character corruption", () => {
+      const runtimeNames = Object.keys(AGENT_DISPLAY_NAMES).map(getAgentRuntimeName)
+      const invisibleCharsRegex = /[\u200B\u200C\u200D\uFEFF]/
+
+      for (const name of runtimeNames) {
+        expect(invisibleCharsRegex.test(name)).toBe(false)
+      }
+    })
+
+    it("only adds leading whitespace, never trailing or interior whitespace beyond the display name", () => {
+      const sisyphus = getAgentRuntimeName("sisyphus")
+      const hephaestus = getAgentRuntimeName("hephaestus")
+      const prometheus = getAgentRuntimeName("prometheus")
+      const atlas = getAgentRuntimeName("atlas")
+
+      for (const name of [sisyphus, hephaestus, prometheus, atlas]) {
+        const trimmed = name.trimStart()
+        expect(name.length).toBeGreaterThanOrEqual(trimmed.length)
+        expect(trimmed.endsWith(" ")).toBe(false)
+      }
+    })
+  })
+})