[Improvement]: Add more content about Lines of Code metrics (#58252)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Laura Coursen <lecoursen@github.com>

content/copilot/reference/copilot-usage-metrics/copilot-usage-metrics.md

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+---
+title: Data available in Copilot usage metrics
+allowTitleToDifferFromFilename: true
+shortTitle: Copilot usage metrics data
+intro: 'You can display and export {% data variables.product.prodname_copilot_short %} usage metrics data in the dashboard and via APIs.'
+permissions: Enterprise owners and billing managers
+versions:
+  fpt: '*'
+  ghec: '*'
+type: reference
+topics:
+  - Copilot
+  - Enterprise
+---
+
+{% data reusables.copilot.usage-metrics-preview %}
+
+The {% data variables.product.prodname_copilot_short %} usage metrics dashboard and APIs display and export data using a consistent set of fields. This reference lists all available metrics and describes how to interpret their values in both dashboard visuals and NDJSON or API exports.
+
+For guidance on how to read and interpret these metrics, see [AUTOTITLE](/copilot/concepts/copilot-metrics).
+
+## Dashboard metrics
+
+These metrics appear directly in the {% data variables.product.prodname_copilot_short %} usage dashboard.
+
+| Metric | Description |
+|:--|:--|
+| Agent adoption | Percentage of {% data variables.product.prodname_copilot_short %}-licensed active users who tried an agent in the current calendar month. |
+| Average chat requests per active user | Average number of chat requests per active user. |
+| Code completions (suggested/accepted) | Total number of inline code suggestions shown and accepted. |
+| Code completion acceptance rate | Percentage of suggestions accepted by users. |
+| Daily active users | Number of unique users who used {% data variables.product.prodname_copilot_short %} on a given day. |
+| Weekly active users | Number of unique users who used {% data variables.product.prodname_copilot_short %} during a seven-day window. |
+| Total active users | Licensed users active in the current calendar month. |
+| Language usage | Distribution of programming languages used with {% data variables.product.prodname_copilot_short %}. |
+| Language usage per day | Daily breakdown of languages used. |
+| Model usage | Distribution of AI models used for chat. |
+| Model usage per day | Daily breakdown of chat model usage. |
+| Model usage per chat mode | Model usage by {% data variables.product.prodname_copilot_short %} feature (Ask, Edit, Agent). |
+| Model usage per language | Distribution of languages broken down by model. |
+| Most used chat model | The most frequently used chat model in the current calendar month. |
+| Requests per chat mode | Number of chat requests by mode (Ask, Edit, Agent). |
+
+## API and export fields
+
+These fields appear in the exported NDJSON reports and in the {% data variables.product.prodname_copilot_short %} usage metrics APIs.
+They provide granular daily records for each user in the enterprise.
+
+| Field | Description |
+|:--|:--|
+| `agent_edit` | A dedicated bucket in the API and reports. Captures lines added and deleted directly by {% data variables.product.prodname_copilot_short %} Agent and Edit mode.<br>These are not included in suggested metrics, since agent edits don’t follow a simple suggestion to acceptance flow. |
+| `report_start_day` / `report_end_day` | Start and end dates for the 28-day reporting period. |
+| `day` | Calendar day this record represents. |
+| `enterprise_id` | Unique ID of the enterprise or organization. |
+| `user_id` / `user_login` | Unique identifier and {% data variables.product.github %} username for the user. |
+| `user_initiated_interaction_count` | Number of explicit prompts sent to {% data variables.product.prodname_copilot_short %}.<br><br> Only counts messages or prompts actively sent to the model. Does **not** include opening the chat panel, switching modes (for example, Ask, Edit, or Agent), using keyboard shortcuts to open the inline UI, or making configuration changes. |
+| `code_generation_activity_count` | Number of distinct {% data variables.product.prodname_copilot_short %} output events generated. <br><br> **Includes:** All generated content, including comments and docstrings. <br> **Multiple blocks:** Each distinct code block from a single user prompt counts as a separate generation. <br> **Note:** This metric is not directly comparable to `user_initiated_interaction_count`, since one prompt can produce multiple generations. |
+| `code_acceptance_activity_count` | Number of suggestions or code blocks accepted by users. <br><br> **Counts:** All built-in accept actions, such as “apply to file,” “insert at cursor,” “insert into terminal,” and use of the **Copy** button. <br> **Does not count:** Manual OS clipboard actions (for example, <kbd>Ctrl</kbd>+<kbd>C</kbd>). <br> **Granularity:** Each acceptance action increments the count once, regardless of how many code blocks were generated by the initial prompt. |
+| `loc_suggested_to_add_sum` | Lines of code {% data variables.product.prodname_copilot_short %} suggested to add (completions, inline chat, chat panel, etc.; **excludes** Agent edits). |
+| `loc_suggested_to_delete_sum` | Lines of code {% data variables.product.prodname_copilot_short %} suggested to delete (future support planned). |
+| `loc_added_sum` | Lines of code actually added to the editor (accepted completions, applied code blocks, agent/edit mode). |
+| `loc_deleted_sum` | Lines of code deleted from the editor (currently from Agent edits). |
+| `totals_by_ide` | Breakdown of metrics by IDE used. |
+| `totals_by_feature` | Breakdown of metrics by {% data variables.product.prodname_copilot_short %} feature (e.g., inline chat, chat panel). |
+| `totals_by_language_feature` | Breakdown combining language and feature dimensions. |
+| `totals_by_model_feature` / `totals_by_language_model` | Model-specific breakdowns for chat activity (not completions). |
+| `last_known_ide_version` / `last_known_plugin_version` | The most recent IDE and {% data variables.copilot.copilot_chat_short %} extension version detected for each user. |