update-config-document

# Update Configuration Documentation Given a new or changed key in `subx-core/src/config/`, confirm the coverage matrix in `docs/config-usage-analysis.md` has a row for it and that the row's status is correct. > **The call-hierarchy line numbers in this document are a dated historical > record and are NOT maintained** — the document's own header declares this. > Do not re-derive or "refresh" them; doing so reverses the document's > declared demotion. Current behaviour lives in `docs/configuration-guide.md`. ## Target Files - **Primary document to update:** `docs/config-usage-analysis.md` - **Secondary document to update (after primary is done):** `README.md` - **Source of truth for configuration items:** `subx-core/src/config/` (structs, defaults, validation — the configuration crate half of the two-crate split) and all their consumers across `subx-core/src/` and `src/` (the CLI half). ## Workflow Work **one configuration item at a time**. Do not batch updates across items. ### 1. Read the Current Document Load `docs/config-usage-analysis.md` first. Treat its existing contents as **potentially outdated**; every field must be re-verified against the code. ### 2. For Each Configuration Item, Do All of the Following 1. **Verify correctness and relevance.** Confirm the item still exists in `subx-core/src/config/` with the same name, type, default, and semantics. 2. **Identify the real "Actual Usage Location".** - Search for every production call site that reads the value. - Follow the chain: when a config value is assigned to a struct field, continue searching for uses of that struct field. A field that is written but never read is effectively **unused** — flag it. - **Ignore all references that appear only in unit tests, integration tests, test helpers, `#[cfg(test)]` blocks, or the `tests/` directory.** Only production-level usage counts. 3. **Exclude items that are obviously set only through the `subx-cli config` subcommand.** These CLI-plumbing entries do not need their own doc row. 4. **Update the document immediately** after verifying this item. Do **not** accumulate edits across multiple items — commit each correction to the file as soon as it is established. This keeps progress auditable and recoverable if the session is interrupted. ### 3. Discover Undocumented Items Scan `subx-core/src/config/` for configuration fields that are **not** represented in `docs/config-usage-analysis.md`. For every missing item, append a new entry following the existing document's format and conventions. ### 4. Sync the README Once every configuration item has been validated and the document fully reflects the current code, update `README.md` so the subcommand and configuration user-facing documentation matches the audited matrix. ## Rules and Reminders - All documentation updates are written in **English**, matching the project convention for docs and code comments. - Do not mark items as deprecated. If a configuration item is no longer used in production, report it to the user for removal instead of silently keeping a dead entry. - Never rewrite the call-tree ("呼叫樹") blocks: their line numbers are the dated record described above. A new row records its usage sites by path and function, not by line number. - Proceed methodically and incrementally: verify, update the doc, move on.