ci: track PR age and idle time with weekly follow-ups

.github/AGENTS.md

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+<!--
+SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+SPDX-License-Identifier: Apache-2.0
+-->
+
+# Automation boundaries
+
+- PR reminders apply only to open, non-draft PRs; recheck immediately before posting.
+- Derive merge readiness from the PR's checks, reviews and mergeability, not a manually maintained Project status.
+- Keep elapsed PR age distinct from inactivity and observed merge-readiness duration.
+- Public PR comments and workflow summaries must not expose private Project notes or fields.
+- Automation documentation describes current behavior and operation; omit development history, machine-specific details and board snapshots.

.github/scripts/PR_TRIAGE.md

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+<!--
+SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+SPDX-License-Identifier: Apache-2.0
+-->
+
+# PR triage metrics and reminders
+
+The [Refresh PR triage workflow](../workflows/project-triage.yml) runs daily at
+16:43 UTC from the default branch. It updates open PRs in the configured Project
+and repository. Archived items, issues, closed PRs and merged PRs are skipped.
+Draft PRs receive metric updates but no reminders.
+
+## Metrics
+
+- **Idle**: full 24-hour periods since the latest human comment, submitted
+  review, inline review comment, or human-linked commit's committer timestamp.
+  Falls back to PR creation. Bot activity, CI, reminder comments and edits to
+  existing comments do not reset it. Commit timestamps do not identify push times.
+- **Age**: full 24-hour periods since PR creation.
+- **Ready days / Ready since**: time since first observing the current head
+  as non-draft, mergeable, `CLEAN`, review `APPROVED` and check rollup `SUCCESS`.
+  A new head, an unmet condition, or an observation gap exceeding 48 hours resets
+  the clock. Daily observations cannot establish readiness before the first run
+  or detect every transition between runs.
+- **Triage state**: automation-managed readiness observations. Invalid values
+  restart the readiness clock.
+
+Missing fields are created automatically. Age is added after Idle in table
+views that show Idle, unless Age is already visible; existing column order is
+preserved.
+
+## Reminders
+
+Only open, non-draft PRs receive reminders after either threshold:
+
+- Observed ready to merge for at least 7 consecutive days.
+- Created more than 14 days ago, regardless of recent activity.
+
+Thresholds use calendar days. Both reasons share one comment and a seven-day
+cooldown. Eligibility is checked again before posting. The workflow never merges
+or closes PRs.
+
+Comments mention assignees, otherwise requested reviewers. Merge-ready PRs
+fall back to approving reviewers, then the author. Other PRs fall back to the
+author. Comments use public PR data only.
+
+## Operation
+
+In **Actions → Refresh PR triage → Run workflow**, select the default branch.
+Manual runs preview by default; enable `apply` to update fields and additionally
+enable `notify` to send reminders. Scheduled runs enable both. GitHub schedules
+may be delayed. Failed API requests fail the run; completed updates remain.
+
+The repository secret `PROJECT_WRITE_TOKEN` requires the `project` scope,
+organization authorization and write access to the Project. It is used only for
+Project requests. The workflow's `GITHUB_TOKEN` reads PR data and posts comments
+with `pull-requests: write`. PR-triggered jobs run tests without Project credentials.
+
+Run tests from the repository root:
+
+```sh
+python3 -m unittest discover -s tests/python/automation -v
+```
+
+For a local preview, provide `PROJECT_TOKEN` and `REPO_TOKEN` in the environment:
+
+```sh
+python3 .github/scripts/project_triage.py --report /tmp/triage-report.json
+```
+
+Add `--apply` to update fields; `--notify` also requires `--apply` and posts reminders.
+The preview report contains per-PR metrics; workflow summaries show counts only.