Enhance issue triage guidelines in CONTRIBUTING.md (flutter#409)

* Enhance issue triage guidelines in CONTRIBUTING.md

Added detailed guidelines for daily and periodic issue triage processes.

* Update CONTRIBUTING.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update CONTRIBUTING.md

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Reformat issue triage instructions for clarity

* Add link to replace the TODO

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 2 people

CONTRIBUTING.md

@@ -19,8 +19,41 @@ To run a script in `tool/`, open the script in VSCode and press ⇧⌘B.
 
 ## Issue triage
 
-We regularly triage issues by looking at newly filed issues and determining what
-we should do about each of them. Triage issues as follows:
+### Daily front-line triage
+
+The function of the daily front-line triage is to determine if the issue
+is a _critical_ issue that needs immediate response.
+
+Until the genui package is marked as 1.0,
+an issue is _critical_ if it blocks someone from compiling the
+package's code as part of their build process, or if previously
+advertised behavior breaks in surprising ways (a behavior change
+is not surprising if it was documented as part of the release
+of the package).
+We note that _critical_ issues should be very rare.
+
+We have a rotation which runs daily on business days. The responsibilities
+of the front-line triage include:
+
+* Once a day, open the list of new issues which do not have
+  [`front-line-handled` label][for-front-line].
+* Assess if this issue is _critical_ (using the definition above).
+  If so, assign P0 label and add the `front-line-handled` label. Then,
+  ping the team chat, cc the Eng Manager, and share that a new P0
+  regression / issue has been identified. In addition, reply to the issue
+  to acknowledge that we believe this is a P0 issue and thank the
+  author for their time.
+* If the issue is not _critical_ and thus not a P0, then add
+  the `front-line-handled` label to the issue. This signals that you have
+  looked at the issue as part of front-line triage.
+* If the issue looks legitimate, feel free to thank the author
+  of the issue for their time. If a follow-up question is warranted,
+  feel free to ask a follow-up question to help the second-line
+  triage process.
+
+### Periodic second-line triage
+
+### Bi-weekly during the planning meeting
 
 Check that existing issues are labeled and organized appropriately:
 
@@ -29,24 +62,29 @@ Check that existing issues are labeled and organized appropriately:
 * Set a milestone to all [P0 and P1 issues][p0_p1_issues_without_milestone].
 * Add all [projectless open issues][projectless_open_issues] to the "genui" project.
 
-Triage new issues:
+### Weekly during the planning meeting
 
-* Open the [list of untriaged issues][untriaged_list].
-* For each issue in the list, do one of:
-  * If we don't plan to fix the issue, close it with an explanation.
-  * If we plan to fix the issue assign a priority label:
-    [P0][P0], [P1][P1], [P2][P2], or [P3][P3]. If you don't know which priority
-    to assign, apply `P2`. If an issue is `P0` or `P1`, add it to a milestone.
+Triage issues ready for second-line review:
+
+* Open the [list of issues ready for second-line][ready-for-second-line].
+* For each issue in the list:
+  * Do one of:
+    * If we don't plan to fix the issue, close it with an explanation.
+    * If we plan to fix the issue assign a priority label:
+      [P0][P0], [P1][P1], [P2][P2], or [P3][P3]. If you don't know which priority
+      to assign, apply `P2`. If an issue is `P0` or `P1`, add it to a milestone.
+  * Add a label for `second-line-triaged`
 
 At the end of a triage session, the untriaged issue list should be as close to
 empty as possible.
 
+[for-front-line]: https://github.com/flutter/genui/issues?q=is%3Aissue%20state%3Aopen%20-label%3AP0%20%20-label%3AP1%20-label%3AP2%20%20-label%3AP3%20-label%3Afront-line-handled
 [flutter_guidelines]: https://github.com/flutter/flutter/blob/master/CONTRIBUTING.md
 [usage_md]: packages/flutter_genui/USAGE.md#configure-firebase
 [assigned_p2_p3_issues]: https://github.com/flutter/genui/issues?q=is%3Aopen%20is%3Aissue%20label%3AP2%2CP3%20assignee%3A*
 [p0_p1_issues_without_milestone]: https://github.com/flutter/genui/issues?q=is%3Aopen%20is%3Aissue%20label%3AP1%2CP0%20no%3Amilestone
 [projectless_open_issues]: https://github.com/flutter/genui/issues?q=is%3Aopen%20is%3Aissue%20no%3Aproject
-[untriaged_list]: https://github.com/flutter/genui/issues?q=is%3Aissue%20state%3Aopen%20-label%3AP0%20%20-label%3AP1%20-label%3AP2%20%20-label%3AP3
+[ready-for-second-line]: https://github.com/flutter/genui/issues?q=is%3Aissue%20state%3Aopen%20label%3Afront-line-handled%20-label%3Asecond-line-triaged
 [P0]: https://github.com/flutter/genui/labels?q=P0
 [P1]: https://github.com/flutter/genui/labels?q=P1
 [P2]: https://github.com/flutter/genui/labels?q=P2