Add back CCR custom instructions note (#59628)

Author: saritai

content/copilot/concepts/prompting/response-customization.md

@@ -93,6 +93,8 @@ Here are some common use cases and examples for each type of custom instructions
   * Preferred language for a company which exclusively speaks a single language: `Always respond in Portuguese.`
   * Organization-wide preferences: `Do not generate code blocks in responses.`
 
+{% data reusables.copilot.code-review.custom-instructions-limit %}
+
 {% data reusables.copilot.custom-instructions-effective %}
 
 ## Next steps

content/copilot/tutorials/use-custom-instructions.md

@@ -45,6 +45,8 @@ Before writing custom instructions, it's helpful to understand how {% data varia
 * **Context limits**: Very long instruction files may result in some instructions being overlooked.
 * **Specificity matters**: Clear, specific instructions work better than vague directives.
 
+{% data reusables.copilot.code-review.custom-instructions-limit %}
+
 Keep these factors in mind as you write your instructions—they'll help you set realistic expectations and write more effective guidance.
 
 ## Writing effective custom instructions

data/reusables/copilot/code-review/custom-instructions-information.md

@@ -6,6 +6,8 @@ You can also write instructions that {% data variables.product.prodname_copilot_
 
 For more information, see [AUTOTITLE](/copilot/customizing-copilot/adding-repository-custom-instructions-for-github-copilot).
 
+{% data reusables.copilot.code-review.custom-instructions-limit %}
+
 ### Example
 
 This example of a `.github/copilot-instructions.md` file contains three instructions that will be applied to all {% data variables.copilot.copilot_code-review_short %}s in the repository.

data/reusables/copilot/code-review/custom-instructions-limit.md

@@ -0,0 +1,2 @@
+> [!NOTE]
+> {% data variables.copilot.copilot_code-review_short %} only reads the first 4,000 characters of any custom instruction file. Any instructions beyond this limit will not affect the reviews generated by {% data variables.copilot.copilot_code-review_short %}. This limit does not apply to {% data variables.copilot.copilot_chat_short %} or {% data variables.copilot.copilot_coding_agent %}.