bugfix: remove CLAUDE_SESSION_ID from env file to prevent corruption

Author: cowwoc

.cat/issues/v2/v2.1/remove-claude-session-id-from-inject-env/STATE.md

@@ -1,6 +1,8 @@
 # State
 
-- **Status:** open
-- **Progress:** 0%
+- **Status:** closed
+- **Resolution:** implemented
+- **Progress:** 100%
 - **Dependencies:** []
 - **Blocks:** []
+- **Target Branch:** v2.1

client/src/main/java/io/github/cowwoc/cat/hooks/session/InjectEnv.java

@@ -26,9 +26,9 @@
 /**
  * Persists Claude environment variables into CLAUDE_ENV_FILE for Bash tool invocations.
  * <p>
- * Appends {@code CLAUDE_PROJECT_DIR}, {@code CLAUDE_PLUGIN_ROOT}, and
- * {@code CLAUDE_SESSION_ID} to the env file so they are available in all subsequent
- * Bash tool calls.
+ * Appends {@code CLAUDE_PROJECT_DIR} and {@code CLAUDE_PLUGIN_ROOT} to the env file so they are available in all
+ * subsequent Bash tool calls. {@code CLAUDE_SESSION_ID} is injected natively by Claude Code (v2.1.77+) and must
+ * not be written here — writing it would corrupt sibling session env files when multiple sessions run concurrently.
  * <p>
  * Only writes for new sessions (source="startup"). On resumed (source="resume") or
  * compacted (source="compact") sessions, the env file already has the correct content
@@ -95,10 +95,8 @@ public Result handle(HookInput input)
     String pluginRoot = scope.getClaudePluginRoot().toString();
     validateEnvValue(projectPath, "CLAUDE_PROJECT_DIR");
     validateEnvValue(pluginRoot, "CLAUDE_PLUGIN_ROOT");
-    validateEnvValue(sessionId, "CLAUDE_SESSION_ID");
     String content = "export CLAUDE_PROJECT_DIR=\"" + projectPath + "\"\n" +
-      "export CLAUDE_PLUGIN_ROOT=\"" + pluginRoot + "\"\n" +
-      "export CLAUDE_SESSION_ID=\"" + sessionId + "\"\n";
+      "export CLAUDE_PLUGIN_ROOT=\"" + pluginRoot + "\"\n";
 
     try
     {
@@ -214,7 +212,7 @@ private String writeToResumedSessionDir(Path sessionEnvBase, Path envPath, Strin
    * <p>
    * After {@code /clear}, Claude Code's session env loader may cache files from an old session directory and not
    * re-read from the new session directory. Writing to all sibling directories ensures that whichever directory the
-   * cache reads from, it gets the current {@code CLAUDE_SESSION_ID}.
+   * cache reads from, it gets the current {@code CLAUDE_PROJECT_DIR} and {@code CLAUDE_PLUGIN_ROOT}.
    *
    * @param sessionEnvBase the parent directory containing all session-env subdirectories
    * @param envPath the CLAUDE_ENV_FILE path (used to identify the already-written directory)

client/src/test/java/io/github/cowwoc/cat/hooks/test/SessionStartHookTest.java

@@ -211,7 +211,8 @@ public void injectEnvWritesToMultipleSessionDirs() throws IOException
         Path siblingEnvFile = siblingDir.resolve("sessionstart-hook-1.sh");
         requireThat(Files.exists(siblingEnvFile), "siblingEnvFileExists").isTrue();
         String siblingContent = Files.readString(siblingEnvFile);
-        requireThat(siblingContent, "siblingContent").contains("CLAUDE_SESSION_ID=\"" + sessionId + "\"");
+        requireThat(siblingContent, "siblingContent").doesNotContain("CLAUDE_SESSION_ID=");
+        requireThat(siblingContent, "siblingContent").contains("CLAUDE_PROJECT_DIR=");
       }
       finally
       {
@@ -300,17 +301,18 @@ public void injectEnvSkipsAlreadyWrittenDir() throws IOException
         // File should exist but should not be double-written (appended twice)
         requireThat(Files.exists(envFile), "envFileExists").isTrue();
         String content = Files.readString(envFile);
-        // Count occurrences of CLAUDE_SESSION_ID - should appear exactly once
+        requireThat(content, "content").doesNotContain("CLAUDE_SESSION_ID=");
+        // CLAUDE_PROJECT_DIR should appear exactly once (not duplicated by double-write)
         int count = 0;
-        int idx = 0;
-        idx = content.indexOf("CLAUDE_SESSION_ID", idx);
-        while (idx != -1)
+        int index = 0;
+        index = content.indexOf("CLAUDE_PROJECT_DIR", index);
+        while (index != -1)
         {
           ++count;
-          ++idx;
-          idx = content.indexOf("CLAUDE_SESSION_ID", idx);
+          ++index;
+          index = content.indexOf("CLAUDE_PROJECT_DIR", index);
         }
-        requireThat(count, "sessionIdOccurrences").isEqualTo(1);
+        requireThat(count, "projectDirOccurrences").isEqualTo(1);
       }
       finally
       {