docs(#4467): document fallow's structural-pre-pass has no upper-bound scope (#4574)

* docs(#4467): document fallow's structural-pre-pass has no upper-bound scope

structural-pre-pass.md's FALLOW_SCOPE_ARGS=(--changed-since "$FALLOW_BASE")
derives a correct, phase-anchored LOWER bound (lockstep with Tier 3's own
scope step, #3995), but fallow's --changed-since is one-sided by design --
verified against fallow 2.70.0's own --help: the only other scoping flags
are --changed-workspaces (workspace selection, not a file range) and
--diff-file (its own help text scopes it to line-range refinement within
the hot-path-touched verdict, not general file selection; gsd-core never
uses it). Reviewing an earlier phase after a later one has landed pulls
the later phase's files into the earlier phase's structural audit.

Not fixable inside this file: fixing fallow itself is a third-party
concern, and working around it (e.g. auditing from a temporary worktree
checked out at the phase tip) is disproportionate machinery for what is
supplementary structural-analysis context, not a blocking gate -- both
routes the issue's own analysis already ruled out. Documented the
asymmetry at the point the scope is derived instead, so a future reader
does not assume this step's tip agrees with Tier 3's just because the
base does.

No regression test: documentation-only, no runtime behavior change.

A prior revision of this commit carried an Emitted-Drift-Ack-Growth
trailer for this growth -- gsd-test's own emitted-attribution check
rejected it as stale ("written or reworded in THIS diff, but nothing
here needed them"), meaning this file (nested under
gsd-core/workflows/code-review/steps/, unlike a top-level
gsd-core/workflows/*.md file) is not tracked by that specific growth
conservation law. Removed the now-confirmed-unnecessary trailer rather
than guess again -- the test's own verdict is authoritative here, not
a re-derivation of its tracked-path rules.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* docs(#4467): backfill changeset PR number

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: sim <sim@local>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

.changeset/sharp-bears-roar.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4574
+---
+**Structural pre-pass now documents that its fallow scope has no upper bound** — the phase-directory-anchored base is correct and lockstep with Tier 3's own scope step, but nothing bounds the tip, so reviewing an earlier phase after a later one has landed could silently pull the later phase's files into the audit. The limitation is now documented at the point the scope is derived.

gsd-core/workflows/code-review/steps/structural-pre-pass.md

@@ -31,6 +31,13 @@ FALLOW_STDERR_TMP=$(mktemp)
 # scope step (#3191/#3995): base = the parent of the first commit that added
 # anything under the phase's own directory. Commit subjects carry no milestone
 # bound — a same-numbered phase in a previous milestone used to win the grep.
+# #4467: the BASE half above is lockstep with Tier 3 (#3995); the TIP is not.
+# fallow's own --changed-since is one-sided by design (no upper-bound flag
+# exists in fallow 2.70.0 — --diff-file only scopes line ranges within the
+# hot-path-touched verdict, it is not a general file-scoping control), so
+# reviewing an earlier phase after a later one has landed pulls the later
+# phase's files into this pass's audited set. Do not assume this step and
+# Tier 3's scope step agree on the tip just because they agree on the base.
 FALLOW_SCOPE_ARGS=()
 if [ \"$FALLOW_SCOPE\" = \"phase\" ]; then
   # #3995: phase-directory anchor — same derivation as the Tier-3 scope step