diff --git a/dev/guidelines/backend/python.md b/dev/guidelines/backend/python.md
index e674b24525..476ab30704 100644
--- a/dev/guidelines/backend/python.md
+++ b/dev/guidelines/backend/python.md
@@ -267,6 +267,22 @@ async def set(self, key: str, value: str, expires: KVTTL | int | None = None) ->
 
 To branch on or read from a typed object, use `isinstance` so the type checker can narrow it; reaching for `getattr(obj, "attr", default)` defeats type analysis. When guarding a schema object, cover the whole family that carries the attribute — `isinstance(schema, (NodeSchema, ProfileSchema, TemplateSchema))` — since profiles and templates inherit node behavior and a `NodeSchema`-only check silently drops them.
 
+### `str` satisfies `Sequence` — exclude it before narrowing
+
+When a parameter accepts `T | Sequence[T] | ...` and `isinstance(data, Sequence)` (or `Iterable`/`Collection`) is how the code tells "one item" from "many", check `str` first whenever `T` includes `str`. A bare string satisfies `Sequence` in its own right, so without the carve-out it falls into the "many" branch and gets iterated character-by-character instead of treated as a single item — silently, if the single-item branch also accepts `str`.
+
+```python
+# ❌ Bad - a bare id like "abc-123" satisfies Sequence and gets shredded into one item per character
+if not isinstance(data, Sequence):
+    data = [data]
+
+# ✅ Good - str is excluded first, so a single id stays a single item
+if isinstance(data, str) or not isinstance(data, Sequence):
+    data = [data]
+```
+
+This carve-out is easy to lose exactly when it matters most: widening a parameter from an invariant `list[T]` to a covariant `Sequence[T]` (e.g. to drop a call-site `# type: ignore[arg-type]`, see [When a wrong-type bug slips through](#when-a-wrong-type-bug-slips-through)) means widening this runtime check in step — an annotation that newly accepts `str` as a `Sequence` while the `isinstance` check still assumes only `list` reaches it will misroute every bare string. Add a test for both the bare-`str` case and the newly-accepted non-`list` sequence (e.g. a `tuple`).
+
 ### Deterministic serialization for hashes and cache keys
 
 When a JSON string feeds a hash, fingerprint, or cache key, its output must be deterministic. Do **not** pass `default=str` to `json.dumps` there: it silently serializes unexpected types via `str()`, which can embed run-specific data (memory addresses) and break determinism. Serialize an explicit, canonical shape (sorted keys, known field types) and let unknown types raise instead of being coerced.
diff --git a/dev/guidelines/changelog.md b/dev/guidelines/changelog.md
index e174049d4d..c9d25c5e44 100644
--- a/dev/guidelines/changelog.md
+++ b/dev/guidelines/changelog.md
@@ -50,6 +50,14 @@ uv run towncrier create -c "Added breadcrumb navigation for hierarchical schemas
 uv run towncrier create -c "Updated dependencies to latest versions" +deps-update.housekeeping.md
 ```
 
+## When to Skip
+
+Skip the fragment entirely when the change has **no user-facing effect** — an internal
+type-annotation correction, a refactor with no behavior change, cleanup of internal docs or
+spec-kit scaffolding. `housekeeping` is for internal changes a user could still plausibly notice
+(a dependency bump, a tooling change) — it is not a catch-all for anything code-adjacent. If it's
+unclear whether a change is user-facing, ask rather than defaulting to adding a fragment.
+
 ## Writing Good Changelog Messages
 
 - Write from the user's perspective
diff --git a/dev/guidelines/git-workflow.md b/dev/guidelines/git-workflow.md
index 65056f532c..c1aba1d8ce 100644
--- a/dev/guidelines/git-workflow.md
+++ b/dev/guidelines/git-workflow.md
@@ -110,6 +110,13 @@ Add changelog fragments to `changelog/` using Towncrier. See [Changelog Guidelin
 - Any notable implementation details
 - Testing performed
 
+**Scope to match the change:** for a trivial, code-only fix with no behavior change (e.g. a
+type-annotation correction), ship just the code diff. Don't carry the spec-kit design record
+(`dev/specs/<feature>/`, see [Repository Organization](repository-organization.md)) or a
+changelog fragment with no user-facing effect (see [When to Skip](changelog.md#when-to-skip))
+into the PR — trim them before opening it if the workflow that produced the change generated them
+by default.
+
 ## Critical Rules
 
 - Never force push to `stable` or `develop`
diff --git a/dev/guidelines/repository-organization.md b/dev/guidelines/repository-organization.md
index 43edf40b4e..7893c95a74 100644
--- a/dev/guidelines/repository-organization.md
+++ b/dev/guidelines/repository-organization.md
@@ -85,6 +85,12 @@ Each directory in `dev/` serves a specific purpose and follows a content lifecyc
 - Moved to `knowledge/` (if describing how something works)
 - Moved to `guidelines/` (if describing how to use something)
 
+**Proportionality**: Not every change needs a spec. If the actual code change is small enough to
+be self-explanatory (e.g. an annotation-only fix, a one-line correction with no behavior change),
+skip the spec-kit scaffolding entirely or trim `dev/specs/<feature>/` from the PR before it goes
+to review — the design record should be proportional to the change it documents, not a fixed-cost
+byproduct of running the workflow. See [Git Workflow → Pull Requests](git-workflow.md).
+
 ### guidelines/
 
 **Purpose**: "What rules should I follow?"