docs(adr): ADR-0027 also covers pre-implementation scoping notes

The scoping workflow (#42/#43 synthesis) flagged #79's open question:
does docs/plans/ cover non-milestone design notes, or only per-milestone
plans? Broaden the category to both — a milestone plan OR a scoping note
for not-yet-scheduled work (e.g. the Phase-3 privsep scoping note from
#43). A scoping note is non-authoritative from the start (records a
constraint set + options, never a decision). Banner template gains a
scopes/tracked-in variant and an ADRs/RFCs-or-tracking-issue pointer.
CLAUDE.md's Plan bullet updated to match.

Claude-Session: https://claude.ai/code/session_01BRMdwxsqYQPbjrWB1Cek6o
Signed-off-by: Gonzalo Fleming <gonzafg2@gmail.com>

Author: gonzafg2

CLAUDE.md

@@ -97,11 +97,12 @@ authoritative reference; the operative rules a reviewer applies:
   docs, tests. When unsure which lane a change belongs in, open an issue and
   ask.
 - **Plan** ([`docs/plans/`](docs/plans/)) — a mutable, **non-authoritative**
-  design note accompanying a milestone's implementation ([ADR-0027](docs/adr/0027-docs-plans-governance-category.md)).
-  Post-merge the code, ADRs, and RFCs are authoritative, never the plan.
-  Every plan carries a dated `Governance status` banner pointing at the
-  ADRs/RFCs that hold its locked-in decisions, and **a plan is never the
-  sole record of a locked-in decision** (that always goes to an ADR/RFC).
+  design note: a milestone plan, or a scoping note for future work
+  ([ADR-0027](docs/adr/0027-docs-plans-governance-category.md)). The code,
+  ADRs, and RFCs are authoritative, never the plan. Every plan carries a
+  dated `Governance status` banner pointing at the ADRs/RFCs (or tracking
+  issue) that hold its decisions, and **a plan is never the sole record of
+  a locked-in decision** (that always goes to an ADR/RFC).
 
 ## Contribution conventions
 

docs/adr/0027-docs-plans-governance-category.md

@@ -19,18 +19,19 @@
 
 ## Decision
 
-`docs/plans/` is a **fourth document category**: **mutable, non-authoritative design notes that accompany a milestone's implementation**. Its contract:
+`docs/plans/` is a **fourth document category**: **mutable, non-authoritative design notes**. These are either *milestone plans* that accompany an implementation (the M4/M5 plans) or *pre-implementation scoping notes* that capture the constraint set and options for future work before it is scheduled (e.g. a Phase-3 privilege-separation scoping note; issue #79 asked whether the lane covers such non-milestone notes — it does). Its contract:
 
-1. **Non-authoritative after merge.** A plan guides the work while it is written and merged alongside it, but once the milestone lands the *code, ADRs, and RFCs* are authoritative — not the plan. A plan is retained for its design rationale, not as a source of truth for what the system does.
+1. **Non-authoritative after merge.** A note guides the work while it is written and merged alongside it, but once the work lands the *code, ADRs, and RFCs* are authoritative — not the note. A scoping note for not-yet-scheduled work is non-authoritative from the start: it records a constraint set and options, never a decision. A note is retained for its design rationale, not as a source of truth for what the system does.
 
-2. **A mandatory, dated `Governance status` banner** heads every file in `docs/plans/`, in the same spirit as ADR-0015's errata banners. It states: the date, that the file is non-authoritative post-merge, which milestone it guided, and **which ADRs/RFCs hold the locked-in decisions**. Template:
+2. **A mandatory, dated `Governance status` banner** heads every file in `docs/plans/`, in the same spirit as ADR-0015's errata banners. It states: the date, that the file is non-authoritative, what it guides or scopes, and **which ADRs/RFCs (and/or tracking issue) hold the authoritative decisions**. Template:
 
    ```
    <!--
      Governance status (YYYY-MM-DD):
-     Non-authoritative design note (ADR-0027). Guided <milestone> (PR #NN).
-     Locked-in decisions live in ADRs/RFCs: <list>. This file is retained
-     for rationale and is not a source of truth post-merge.
+     Non-authoritative design note (ADR-0027). <Guided <milestone> (PR #NN)
+     | Scopes <future work>; tracked in #NN>.
+     Authoritative decisions live in ADRs/RFCs: <list, or "none yet">.
+     This file is retained for rationale and is not a source of truth.
    -->
    ```