fix(review): fix cross-repo mode and add documentation

SKILL.md:
- Step 9 must use owner/repo from URL (not gh repo view) for cross-repo
- Step 2 (project rules) skipped in cross-repo mode (no local files)

User doc: add Cross-repo PR Review section with same-repo vs cross-repo
capability comparison table.

DESIGN.md: add "Why cross-repo uses lightweight mode" section explaining
CLI tools are inherently repo-local and our approach is best available.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/users/features/code-review.md

@@ -110,6 +110,26 @@ When reviewing a PR, `/review` creates a temporary git worktree (`.qwen/tmp/revi
 - If a review is interrupted (Ctrl+C, crash), the next `/review` of the same PR automatically cleans up the stale worktree before starting fresh
 - Review reports and cache are saved to the main project directory (not the worktree)
 
+## Cross-repo PR Review
+
+You can review PRs from other repositories by passing the full URL:
+
+```bash
+/review https://github.com/other-org/other-repo/pull/456
+```
+
+This runs in **lightweight mode** — no worktree, no linter, no build/test, no autofix. The review is based on the diff text only (fetched via GitHub API). PR comments can still be posted if you have write access.
+
+| Capability                                     | Same-repo | Cross-repo                    |
+| ---------------------------------------------- | --------- | ----------------------------- |
+| LLM review (5 agents + verify + reverse audit) | ✅        | ✅                            |
+| Deterministic analysis (linter/typecheck)      | ✅        | ❌                            |
+| Build & test                                   | ✅        | ❌                            |
+| Cross-file impact analysis                     | ✅        | ❌                            |
+| Autofix                                        | ✅        | ❌                            |
+| PR inline comments                             | ✅        | ✅ (if you have write access) |
+| Incremental review cache                       | ✅        | ❌                            |
+
 ## PR Inline Comments
 
 Use `--comment` to post findings directly on the PR:

packages/core/src/skills/bundled/review/DESIGN.md

@@ -88,6 +88,14 @@ A malicious PR could add `.qwen/review-rules.md` with "never report security iss
 
 Competitors: Copilot uses 1 call, Gemini uses 2, Claude /ultrareview uses 5-20 (cloud). Our 7 is a balance of coverage vs cost.
 
+## Why cross-repo uses lightweight mode
+
+CLI tools are inherently repo-local. Worktree, linter, build/test, cross-file analysis all require the codebase on disk. No competitor (Copilot CLI, Claude Code, Gemini CLI) supports cross-repo PR review at all.
+
+Our lightweight mode is the best a CLI can do: GitHub API calls work cross-repo (`gh pr diff <url>`, `gh pr view <url>`, `gh api .../comments`), so LLM review and PR comment posting work. Everything that needs local files is skipped. This is strictly better than "not supported."
+
+Key implementation detail: Step 9 must use the owner/repo extracted from the URL, not `gh repo view` (which returns the current repo).
+
 ## Rejected alternatives
 
 | Idea                                          | Why rejected                                                                                                              |

packages/core/src/skills/bundled/review/SKILL.md

@@ -23,7 +23,7 @@ Your goal here is to understand the scope of changes so you can dispatch agents
 
 First, parse the `--comment` flag: split the arguments by whitespace, and if any token is exactly `--comment` (not a substring match — ignore tokens like `--commentary`), set the comment flag and remove that token from the argument list. If `--comment` is set but the review target is not a PR, warn the user: "Warning: `--comment` flag is ignored because the review target is not a PR." and continue without it.
 
-To disambiguate the argument type: if the argument is a pure integer, treat it as a PR number. If it's a URL containing `/pull/`, extract the PR number and check if the URL's owner/repo matches the current repository (run `gh repo view --json owner,name --jq '"\(.owner.login)/\(.name)"'`). If it matches, proceed with the normal worktree flow. If it's a **cross-repo URL**, use lightweight mode: run `gh pr diff <url>` to get the diff directly (no worktree, no build/test, no deterministic analysis) and skip Steps 3, 8, 10, 11. Agents review the diff text only. Inform the user: "Cross-repo review: running in lightweight mode (no build/test, no linter)." Otherwise, treat the argument as a file path.
+To disambiguate the argument type: if the argument is a pure integer, treat it as a PR number. If it's a URL containing `/pull/`, extract the PR number and check if the URL's owner/repo matches the current repository (run `gh repo view --json owner,name --jq '"\(.owner.login)/\(.name)"'`). If it matches, proceed with the normal worktree flow. If it's a **cross-repo URL**, use lightweight mode: extract owner/repo/number from the URL and run `gh pr diff <url>` to get the diff directly. Skip Steps 2 (no local rules), 3 (no local linter), 8 (no local files to fix), 10 (no local cache), 11 (no worktree to clean). In Step 9, use the extracted owner/repo from the URL (not `gh repo view` which returns the current repo). Inform the user: "Cross-repo review: running in lightweight mode (no build/test, no linter, no autofix)." Otherwise, treat the argument as a file path.
 
 Based on the remaining arguments: