diff --git a/packages/opencode/src/kilocode/editor-context.ts b/packages/opencode/src/kilocode/editor-context.ts
index 3a087bc82af..b4b1d98b9d6 100644
--- a/packages/opencode/src/kilocode/editor-context.ts
+++ b/packages/opencode/src/kilocode/editor-context.ts
@@ -24,7 +24,7 @@ export function staticEnvLines(ctx?: EditorContext): string[] {
  * user message so the model always has fresh context.
  * Always includes at least the current timestamp.
  */
-function timestamp(): string {
+function datestamp(): string {
   const now = new Date()
   const offset = -now.getTimezoneOffset()
   const sign = offset >= 0 ? "+" : "-"
@@ -33,11 +33,11 @@ function timestamp(): string {
     .padStart(2, "0")
   const m = (Math.abs(offset) % 60).toString().padStart(2, "0")
   const pad = (n: number) => n.toString().padStart(2, "0")
-  return `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}T${pad(now.getHours())}:${pad(now.getMinutes())}:${pad(now.getSeconds())}${sign}${h}:${m}`
+  return `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}${sign}${h}:${m}`
 }
 
 export function environmentDetails(ctx?: EditorContext): string {
-  const lines: string[] = [`Current time: ${timestamp()}`]
+  const lines: string[] = [`Current date: ${datestamp()}`]
   if (ctx?.activeFile) {
     lines.push(`Active file: ${ctx.activeFile}`)
   }
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 3345aca761e..161d035945d 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -78,6 +78,12 @@ export namespace SessionPrompt {
 
   const log = Log.create({ service: "session.prompt" })
 
+  // kilocode_change — persist environment details across loop() invocations so that
+  // older user messages keep their envBlock across turns, preserving the byte-identical
+  // conversation prefix for Anthropic prompt caching.
+  // Key: "sessionID:messageID" → rendered envBlock string.
+  const envCache = new Map<string, string>()
+
   const state = Instance.state(
     () => {
       const data: Record<
@@ -289,6 +295,10 @@ export namespace SessionPrompt {
     }
     match.abort.abort()
     delete s[sessionID]
+    // kilocode_change — clean up envCache entries for this session
+    for (const k of envCache.keys()) {
+      if (k.startsWith(sessionID + ":")) envCache.delete(k)
+    }
     SessionStatus.set(sessionID, { type: "idle" })
     return
   }
@@ -324,12 +334,6 @@ export namespace SessionPrompt {
     // on the user message and will be retrieved from lastUser below
     let structuredOutput: unknown | undefined
 
-    // kilocode_change — cache environment details per turn so the last user
-    // message stays byte-identical across tool-loop steps (prompt caching).
-    // Keyed by user message ID so it recomputes when a new user message arrives.
-    let envBlock: string | undefined
-    let envUser: string | undefined
-
     let step = 0
     const session = await Session.get(sessionID)
     while (true) {
@@ -701,27 +705,33 @@ export namespace SessionPrompt {
 
       await Plugin.trigger("experimental.chat.messages.transform", {}, { messages: msgs })
 
-      // kilocode_change start — ephemerally inject dynamic editor context into last user message
-      if (envUser !== lastUser.id) {
-        envBlock = environmentDetails(lastUser.editorContext)
-        envUser = lastUser.id
+      // kilocode_change start — ephemerally inject dynamic editor context into user messages.
+      // Each user message's envBlock is computed once (when it becomes the last user message)
+      // and preserved across loop() calls via the module-level envCache so the conversation
+      // prefix stays byte-identical for Anthropic prompt caching. Previously, only the *last*
+      // user message received the envBlock, causing earlier user messages to lose theirs on
+      // new turns and invalidating the cached prefix at that position.
+      const key = `${sessionID}:${lastUser.id}`
+      if (!envCache.has(key)) {
+        envCache.set(key, environmentDetails(lastUser.editorContext))
       }
-      if (envBlock) {
-        const idx = msgs.findLastIndex((m) => m.info.role === "user")
-        if (idx !== -1)
-          msgs[idx] = {
-            ...msgs[idx],
-            parts: [
-              ...msgs[idx].parts,
-              {
-                id: Identifier.ascending("part"),
-                sessionID,
-                messageID: msgs[idx].info.id,
-                type: "text",
-                text: envBlock,
-              } satisfies MessageV2.TextPart,
-            ],
-          }
+      for (let i = 0; i < msgs.length; i++) {
+        if (msgs[i].info.role !== "user") continue
+        const env = envCache.get(`${sessionID}:${msgs[i].info.id}`)
+        if (!env) continue
+        msgs[i] = {
+          ...msgs[i],
+          parts: [
+            ...msgs[i].parts,
+            {
+              id: Identifier.ascending("part"),
+              sessionID,
+              messageID: msgs[i].info.id,
+              type: "text",
+              text: env,
+            } satisfies MessageV2.TextPart,
+          ],
+        }
       }
       // kilocode_change end
 
diff --git a/packages/opencode/test/kilocode/editor-context.test.ts b/packages/opencode/test/kilocode/editor-context.test.ts
new file mode 100644
index 00000000000..f2b3da1563c
--- /dev/null
+++ b/packages/opencode/test/kilocode/editor-context.test.ts
@@ -0,0 +1,69 @@
+import { describe, expect, test } from "bun:test"
+import { environmentDetails, staticEnvLines } from "../../src/kilocode/editor-context"
+
+describe("environmentDetails", () => {
+  test("contains date-only timestamp without hours/minutes/seconds", () => {
+    const result = environmentDetails()
+    // Must contain a date line
+    expect(result).toContain("Current date:")
+    // Must NOT contain time-of-day (hours:minutes:seconds pattern like T13:32:40)
+    expect(result).not.toMatch(/Current (?:date|time): \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/)
+    // Must NOT use "Current time:" label at all
+    expect(result).not.toContain("Current time:")
+  })
+
+  test("date matches YYYY-MM-DD+HH:MM format", () => {
+    const result = environmentDetails()
+    expect(result).toMatch(/Current date: \d{4}-\d{2}-\d{2}[+-]\d{2}:\d{2}/)
+  })
+
+  test("is stable across consecutive calls on the same day", () => {
+    const a = environmentDetails()
+    const b = environmentDetails()
+    expect(a).toBe(b)
+  })
+
+  test("wraps in environment_details tags", () => {
+    const result = environmentDetails()
+    expect(result).toMatch(/^<environment_details>\n/)
+    expect(result).toMatch(/<\/environment_details>$/)
+  })
+
+  test("includes active file when provided", () => {
+    const result = environmentDetails({ activeFile: "src/index.ts" })
+    expect(result).toContain("Active file: src/index.ts")
+  })
+
+  test("includes visible files when provided", () => {
+    const result = environmentDetails({ visibleFiles: ["a.ts", "b.ts"] })
+    expect(result).toContain("Visible files:")
+    expect(result).toContain("  a.ts")
+    expect(result).toContain("  b.ts")
+  })
+
+  test("includes open tabs when provided", () => {
+    const result = environmentDetails({ openTabs: ["x.ts", "y.ts"] })
+    expect(result).toContain("Open tabs:")
+    expect(result).toContain("  x.ts")
+    expect(result).toContain("  y.ts")
+  })
+
+  test("omits optional sections when not provided", () => {
+    const result = environmentDetails()
+    expect(result).not.toContain("Active file:")
+    expect(result).not.toContain("Visible files:")
+    expect(result).not.toContain("Open tabs:")
+  })
+})
+
+describe("staticEnvLines", () => {
+  test("includes shell when provided", () => {
+    const result = staticEnvLines({ shell: "/bin/bash" })
+    expect(result).toEqual(["  Default shell: /bin/bash"])
+  })
+
+  test("returns empty array when no context", () => {
+    expect(staticEnvLines()).toEqual([])
+    expect(staticEnvLines({})).toEqual([])
+  })
+})