refactor: move dynamic editor context from system prompt to user message

Split editor context into static and dynamic parts:

- Static (system prompt, cached): date, timezone, shell
  These rarely change and benefit from prompt caching.

- Dynamic (user message, per-turn): active file, visible files, open tabs
  These change frequently as the user switches files/tabs. Injected as a
  synthetic <environment_details> block on each user message so the model
  always has fresh context.

This matches the pattern used by the VS Code extension, where
getEnvironmentDetails() is called before every agent turn.

packages/opencode/src/kilocode/editor-context.ts

@@ -6,36 +6,50 @@ export interface EditorContext {
   timezone?: string
 }
 
-function formatDate(timezone?: string): string[] {
+/**
+ * Build static <env> lines from editor context.
+ * These rarely change during a session and belong in the system prompt
+ * so they benefit from prompt caching.
+ */
+export function staticEnvLines(ctx?: EditorContext): string[] {
   const now = new Date()
   const lines = [`  Today's date: ${now.toDateString()}`]
-  if (timezone) {
+  if (ctx?.timezone) {
     const offset = -now.getTimezoneOffset()
     const sign = offset >= 0 ? "+" : "-"
     const hours = Math.floor(Math.abs(offset) / 60)
     const mins = Math.abs(offset) % 60
-    lines.push(`  User timezone: ${timezone}, UTC${sign}${hours}:${mins.toString().padStart(2, "0")}`)
+    lines.push(`  User timezone: ${ctx.timezone}, UTC${sign}${hours}:${mins.toString().padStart(2, "0")}`)
+  }
+  if (ctx?.shell) {
+    lines.push(`  Default shell: ${ctx.shell}`)
   }
   return lines
 }
 
 /**
- * Build additional <env> lines from VS Code editor context.
- * Returns an array of pre-formatted `  key: value` strings.
+ * Build a per-message <environment_details> block from editor context.
+ * These change frequently (user switches files/tabs) and belong in the
+ * user message so the model always has fresh context.
+ * Returns undefined when there is nothing dynamic to report.
  */
-export function editorContextEnvLines(ctx?: EditorContext): string[] {
-  const lines = formatDate(ctx?.timezone)
-  if (ctx?.shell) {
-    lines.push(`  Default shell: ${ctx.shell}`)
-  }
+export function environmentDetails(ctx?: EditorContext): string | undefined {
+  const lines: string[] = []
   if (ctx?.activeFile) {
-    lines.push(`  Active file: ${ctx.activeFile}`)
+    lines.push(`Active file: ${ctx.activeFile}`)
   }
   if (ctx?.visibleFiles?.length) {
-    lines.push(`  Visible files: ${ctx.visibleFiles.join(", ")}`)
+    lines.push(`Visible files:`)
+    for (const f of ctx.visibleFiles) {
+      lines.push(`  ${f}`)
+    }
   }
   if (ctx?.openTabs?.length) {
-    lines.push(`  Open tabs: ${ctx.openTabs.join(", ")}`)
+    lines.push(`Open tabs:`)
+    for (const f of ctx.openTabs) {
+      lines.push(`  ${f}`)
+    }
   }
-  return lines
+  if (lines.length === 0) return undefined
+  return ["<environment_details>", ...lines, "</environment_details>"].join("\n")
 }

packages/opencode/src/session/prompt.ts

@@ -47,6 +47,7 @@ import { iife } from "@/util/iife"
 import { Shell } from "@/shell/shell"
 import { Truncate } from "@/tool/truncation"
 import { PlanFollowup } from "@/kilocode/plan-followup" // kilocode_change
+import { environmentDetails } from "@/kilocode/editor-context" // kilocode_change
 
 // @ts-ignore
 globalThis.AI_SDK_LOG_WARNINGS = false
@@ -1355,6 +1356,20 @@ export namespace SessionPrompt {
       }),
     ).then((x) => x.flat().map(assign))
 
+    // kilocode_change start — inject dynamic editor context into user message
+    const envBlock = environmentDetails(input.editorContext)
+    if (envBlock) {
+      parts.push({
+        id: Identifier.ascending("part"),
+        messageID: info.id,
+        sessionID: input.sessionID,
+        type: "text",
+        text: envBlock,
+        synthetic: true,
+      })
+    }
+    // kilocode_change end
+
     await Plugin.trigger(
       "chat.message",
       {

packages/opencode/src/session/system.ts

@@ -13,7 +13,7 @@ import type { Provider } from "@/provider/provider"
 
 // kilocode_change start
 import SOUL from "../kilocode/soul.txt"
-import { editorContextEnvLines, type EditorContext } from "../kilocode/editor-context"
+import { staticEnvLines, type EditorContext } from "../kilocode/editor-context"
 // kilocode_change end
 
 export namespace SystemPrompt {
@@ -67,7 +67,7 @@ export namespace SystemPrompt {
         `  Working directory: ${Instance.directory}`,
         `  Is directory a git repo: ${project.vcs === "git" ? "yes" : "no"}`,
         `  Platform: ${process.platform}`,
-        ...editorContextEnvLines(editorContext), // kilocode_change
+        ...staticEnvLines(editorContext), // kilocode_change
         `</env>`,
         `<directories>`,
         `  ${