docs: explain how to enable the context window indicator

docs/user/composer.md

@@ -240,7 +240,12 @@ Provider commands must start the message to run. T3 Code commands such as
 `/model` and `/plan`, and skill mentions, work on any line.
 
 Send `/compact` in an existing conversation to reduce context usage when the
-provider supports it. Web and desktop also offer compaction from the context meter.
+provider supports it, even with the context meter turned off.
+
+On web and desktop, turn on **Settings → Labs → Legacy → Context
+window indicator (legacy)** to see context usage. The meter is off by default
+and appears once the provider reports usage. Open it for usage details and
+**Compact context** when the provider supports compaction.
 
 Claude instances can also compact idle threads for you. See
 [compact long conversations](./providers-claude.md#compact-long-conversations).

docs/user/providers-acp.md

@@ -100,7 +100,9 @@ including when another client performs the import.
 
 The thread keeps the native session's title and last-update value as provider metadata without
 overwriting a title you set in T3 Code. Agents that report ACP context usage drive the composer's
-context meter and cumulative cost metadata. Text resources and links render as assistant output;
+context meter and cumulative cost metadata. The meter is off by default; see
+[commands and skills](./composer.md#commands-and-skills) to enable it on web and desktop.
+Text resources and links render as assistant output;
 binary resources, images, and audio that T3 Code cannot render yet appear as explicit placeholders
 instead of disappearing.
 

docs/user/providers-claude.md

@@ -49,8 +49,12 @@ Set **Auto-compact after** in the Claude provider settings to an integer between
 window. Leave it empty for Claude Code's default.
 
 You can also send `/compact` in an existing conversation. Web and desktop offer
-**Compact context** from the context meter. When you return to a large thread
-after Claude's prompt cache expires, a **Compact** chip with the thread's token count shows
+**Compact context** from the context meter. The meter is off by default; see
+[commands and skills](./composer.md#commands-and-skills) to enable it. Claude Code
+compacts automatically whether the meter is on or off.
+
+When you return to a large thread after Claude's prompt cache expires, a
+**Compact** chip with the thread's token count shows
 next to the send button. While it is on, Enter summarizes the history first, then
 sends your message. Click the chip to switch it to **Full** and keep the full
 history for that message. The cache lasts about an hour on a Claude

docs/user/providers-pi.md

@@ -86,5 +86,6 @@ threads.
   environment, including `PI_CODING_AGENT_DIR` if set. Trust the folder or its parent with `/trust`,
   then start a new thread using that same worktree. Launch arguments with `--no-approve` keep
   project files off without the notice.
-- The context meter appears once Pi reports usage for the thread. Some model providers only
-  report usage when a response completes, so the meter can wait for the first reply.
+- The context meter is off by default; see [commands and skills](./composer.md#commands-and-skills)
+  to enable it on web and desktop. It appears once Pi reports usage for the thread. Some model
+  providers only report usage when a response completes, so the meter can wait for the first reply.