feat(spec-phase): surface zero-classification edge-probe requirements as unclassified candidates (#1110) (#1117)

Edge-probe now surfaces a zero-classification requirement (non-empty prose, no
shape cue matched, no `shapes` override) as a single soft `unclassified — review
manually` candidate instead of silently dropping it — the exact blind spot the
probe exists to catch. Dismissible like any edge; the `shapes: []` opt-out stays
silent; `TAXONOMY` (the closed 8 categories) is unchanged. Under `--auto` the
candidate is left `unresolved`, never auto-`backstop` (a missing shape is not
evidence an edge exists).

Closes #1110

gsd-core/workflows/spec-phase.md

@@ -295,6 +295,9 @@ For each Requirement gathered so far:
    - **Dismiss (reason)** → mark `dismissed` with a required non-empty reason.
    - **Backstop with a test** → mark `backstop`; note "held-out edge test" for plan-phase.
    - **Defer** → leave `unresolved`.
+   - An `unclassified` row (probe `unclassified — review manually`) means the requirement's
+     prose matched no shape cue (#1110) — treat it like any other candidate (**Specify**,
+     **Dismiss (reason)**, or **Defer**). A manual-review nudge, not a hard block.
 
 **Soft gate (after resolving):**
 - All applicable edges resolved → proceed to Step 6.
@@ -310,6 +313,14 @@ For each Requirement gathered so far:
 otherwise auto-`backstop` (never auto-dismiss — a wrong dismissal is the exact silent
 failure being eliminated). Log: `[auto] edge coverage: C covered, B backstop, U unresolved`.
 
+**`unclassified` exception (#1110):** `--auto` leaves an `unclassified` candidate
+**`unresolved`** (the soft gate surfaces it as a flagged planner assumption) — it never
+auto-`backstop`s it. A missing shape is not evidence an edge exists, so minting a held-out
+edge obligation on a requirement that may be genuinely edge-free would be a false claim and
+risks a vacuous edge test. Leaving it `unresolved` keeps the zero-cue requirement visible
+(never a silent drop) without fabricating an edge — which is exactly #1110's purpose: surface
+it for review, do not auto-handle it.
+
 Populate the `## Edge Coverage` section of SPEC.md from the resolved edges.
 
 ## Step 5.6: Prohibition-Completeness Probe (must-NOT)