FE-703: Add /planning-pr skill

[kostandinang]

What

Adds a /planning-pr agent skill that captures when planning-doc edits warrant a dedicated PR off main vs an inline commit on a feature branch.

Linear: FE-703 (child of FE-699).

Why

Every paragraph-level rewrite of memory/PLAN.md / memory/SPEC.md competes with feature branches for the same lines on rebase. This skill encodes the project's process-only mitigation: serialize all paragraph-level rewrites and any SPEC.md tracked-ID additions through dedicated planning PRs.

Doesn't preclude the structural fixes drafted under FE-699 (union merge driver, per-frontier-item file decomposition) — this just makes the convention discoverable.

Change

One new file: .agents/skills/planning-pr/SKILL.md (73 lines, no code, no tests).

Test plan

• CI green
• Next /ln-sync invocation routes through this skill before committing

[cursor]

PR Summary

Low Risk
Adds a new process/documentation skill only; no runtime code paths or data/security-sensitive logic are affected.

Overview
Adds a new agent skill doc, planning-pr, that formalizes when edits to memory/PLAN.md/memory/SPEC.md must be split into a separate planning-only PR off main (especially any changes to sequential tracked-ID rows).

Defines the decision threshold, required workflow (Linear → Graphite branch off main → memory/*-only diff → merge before restacking), and lists anti-patterns/entry points to reduce merge conflicts across parallel feature branches.

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[kostandinang]

• FE-703: Add /planning-pr skill #99 👈 (View in Graphite)
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[augmentcode]

🤖 Augment PR Summary

Summary: This PR adds a new planning-pr skill that codifies when planning-document edits should be split into a dedicated “planning PR” off main.

Changes:

• Introduced .agents/skills/planning-pr/SKILL.md describing the decision threshold (one-line tweaks vs paragraph rewrites) and a hard rule for SPEC tracked-ID changes.
• Documented an end-to-end workflow (Linear issue → branch off main → memory/*-only edits → verify → PR → merge → restack downstream).
• Added anti-patterns and common entry points (e.g., after /ln-sync or when conflicts arise in memory/PLAN.md/memory/SPEC.md).

Technical Notes: The skill’s core intent is to serialize high-conflict planning edits by landing them on main first, so feature stacks can rebase onto a shared planning baseline.

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[augmentcode]

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