fix(taskstoissues): skip tasks that already have a GitHub issue (#2992)

* fix(taskstoissues): skip tasks that already have a GitHub issue

Re-running /speckit-taskstoissues created a duplicate issue for every
task because the command never checked for existing ones. Add a
deduplication step before issue creation: list the repo's issues
(state all) via the GitHub MCP server, collect the task IDs already
present in issue titles, and skip any task that already has a matching
issue. Issue titles are now prefixed with the task ID (e.g. T001:) so
they can be matched on later runs, and list_issues is added to the
command's MCP tools.

Fixes #2968

* fix(taskstoissues): correct list_issues usage and issue title format

Address Copilot review:
- list_issues has no 'all' state; omitting state returns both open and
  closed issues. Use cursor-based pagination (after/endCursor) to fetch
  every page before building the dedup set.
- task lines already start with their ID, so reuse the task text as the
  issue title instead of prefixing the ID again (which produced
  'T001: T001 ...').

* fix(taskstoissues): match task IDs anywhere in titles and define one canonical title

Address follow-up Copilot review:
- task lines start with a markdown checkbox (- [ ] T001 ...), so the
  creation step now strips the checkbox and [P]/[US#] markers and writes
  a single canonical title 'T001: <description>'.
- dedup now scans each issue title for a T<digits> token anywhere in the
  title, so existing issues titled 'T001 ...', 'T001: ...' or '[T001] ...'
  are all matched.

* fix(taskstoissues): use word-boundary task ID match and request perPage 100

Address Copilot review:
- match issue titles against \bT\d{3}\b so tokens like ST001 or T0010
  are not matched by mistake (task IDs are T + 3 digits).
- request perPage: 100 on list_issues to reduce pagination calls.

* fix(taskstoissues): bound issue pagination to the tasks being processed

Address Copilot review: extract the task IDs from tasks.md first, then
paginate list_issues only until every task ID has been matched (or pages
run out), instead of fetching the repo's entire issue history. Keeps the
call count bounded on repos with large issue backlogs.

Author: Quratulain-bilal

templates/commands/taskstoissues.md

@@ -1,6 +1,6 @@
 ---
 description: Convert existing tasks into actionable, dependency-ordered GitHub issues for the feature based on available design artifacts.
-tools: ['github/github-mcp-server/issue_write']
+tools: ['github/github-mcp-server/list_issues', 'github/github-mcp-server/issue_write']
 scripts:
   sh: scripts/bash/check-prerequisites.sh --json --require-tasks --include-tasks
   ps: scripts/powershell/check-prerequisites.ps1 -Json -RequireTasks -IncludeTasks
@@ -62,7 +62,10 @@ git config --get remote.origin.url
 > [!CAUTION]
 > ONLY PROCEED TO NEXT STEPS IF THE REMOTE IS A GITHUB URL
 
-1. For each task in the list, use the GitHub MCP server to create a new issue in the repository that is representative of the Git remote.
+1. **Fetch existing issues for deduplication**: Before creating anything, build the set of task IDs you are about to process from `tasks.md` (each is a `T` followed by three digits, e.g. `T001`). Then use the GitHub MCP server's `list_issues` tool to look for issues that already cover those IDs. Do not pass a `state` value, since omitting it makes the tool return both open and closed issues. Request `perPage: 100` to keep the number of calls down, and since the tool uses cursor-based pagination, request pages with the `after` parameter (using the `endCursor` from the previous response). For each issue title, match it against the task ID pattern `\bT\d{3}\b` (word boundaries so tokens like `ST001` or `T0010` are not matched by mistake; this also recognises titles written as `T001 ...`, `T001: ...` or `[T001] ...`) and, when it matches one of your task IDs, mark that ID as already having an issue. Stop paginating as soon as every task ID has been matched, or when there are no more pages, so you do not keep fetching the whole repository's issue history once all task IDs are accounted for. This bounds the number of calls on repos with large issue histories and still prevents duplicates when the command is re-run after `tasks.md` is regenerated or the skill is re-invoked.
+1. For each task in the list, use the GitHub MCP server to create a new issue in the repository that is representative of the Git remote. Task lines in `tasks.md` start with a markdown checkbox, so first strip the leading `- [ ]` (and any `[P]` / `[US#]` markers) to recover the task ID and its description. Create the issue with a single canonical title of the form `T001: <description>`, with the ID written once followed by the task description (for example, the line `- [ ] T001 Create project structure` becomes the title `T001: Create project structure`).
+   - **Skip** any task whose ID is already present in the set of existing issues from the previous step, and report it (for example, `T001 already has an issue, skipping`).
+   - Only create issues for tasks that do not yet have a matching issue.
 
 > [!CAUTION]
 > UNDER NO CIRCUMSTANCES EVER CREATE ISSUES IN REPOSITORIES THAT DO NOT MATCH THE REMOTE URL