enhance(#2229): add three-way claim disposition (admit/refute/abstain) to /gsd-explore research pass (#2543)

Closes #2229.

Each claim surfaced by /gsd-explore's research pass is dispositioned admit, refute, or abstain, with abstentions routed to a visible ledger instead of being smoothed into confident prose. Refute and abstain are separated by whether the disagreeing source is authoritative for that claim; a strong prior is never authoritative alone.

Two guards ride with it: conflict-abstention, and a tier floor that presents a would-be admit as an abstain when the researcher's resolved tier is the budget tier or cannot be determined.

To make that floor enforceable, resolve-model now emits the effective tier (--pick tier). It was already computed above the resolve_model_ids omit gate but was unreachable from a workflow, which left the floor inert on every non-Claude install - the model id is blank under omit and runtime-substituted where a tier map exists, and the profile defaults to balanced. The tier signal mirrors every resolution step that can change which tier runs, including the model_policy preset, and reports unknown rather than guessing. Output is additive; model, profile and effort are unchanged.

Two residuals are disclosed in the workflow rather than papered over: a raw-model-id model_overrides pin reports unknown and is floored (fails closed), and a model_profile_overrides entry repointing a tier at another tier's model can under-report (fails open, and predates this change).

Admin merge used only to satisfy the missing secondary reviewer on a single-maintainer PR. No CI failure and no conflict were bypassed: 38 checks green, remote runner 32255/32255 on both Node lanes.

agents/gsd-phase-researcher.md

@@ -183,6 +183,14 @@ Keep using the provenance tags in RESEARCH.md:
 
 **Never present LOW confidence findings as authoritative.**
 
+**Claim-disposition mode (the `/gsd:explore` quick-research pass).** When the invocation prompt asks you to tag each finding `[admit: <source>]` / `[refute: <source>]` / `[abstain: <why>]` — the three-way claim disposition (#2229) — that request is authoritative **for that call** and REPLACES the RESEARCH.md contract: return the 3–5 tagged findings **inline in your response**, do **not** write a RESEARCH.md file, and do **not** use the *Research Complete* structured return. Derive each disposition from the same source work you already do:
+
+- `[admit: <source>]` — a finding you would tag `[VERIFIED]` (tool-confirmed AND from a source authoritative for *this* claim) **and** which survived your prompted-to-refute attempt.
+- `[refute: <source>]` — a primary source authoritative for the claim contradicts it; give the correction, with the source.
+- `[abstain: <why>]` — everything else: `[ASSUMED]`/LOW, a non-authoritative `[CITED]` source, unverifiable, or a source-vs-prior conflict. `<why>` MUST be one of the caller's five ledger reasons, byte-identical to `explore.md`: `unverifiable` | `source-vs-prior conflict` | `non-authoritative source` | `tier-floor: unearned confidence` | `untagged — disposition not reported` — the last is the caller's to assign, not yours. A "strong prior" alone is never authoritative — it can only abstain, never refute.
+
+Every finding carries **exactly one** tag; an untagged finding is routed to the caller's Unresolved Ledger as `untagged — disposition not reported`. The confidence tier still rides underneath (it drives the caller's tier floor), but the disposition — not the tier — decides what may be stated.
+
 </source_hierarchy>
 
 <verification_protocol>
@@ -843,6 +851,16 @@ Research complete. Planner can now create PLAN.md files.
 [What's needed to continue]
 ```
 
+## Quick Claim-Disposition Pass (`/gsd:explore`)
+
+Not the templates above — an inline return, no RESEARCH.md and no phase/confidence header. 3–5 findings, each on its own line, each carrying exactly one disposition tag (see **Claim-disposition mode**):
+
+```markdown
+- [admit: <source>] <finding that survived refute and is grounded>
+- [refute: <source>] <corrected claim — a primary source contradicts the original>
+- [abstain: <why>] <finding that is unverifiable / non-authoritative / conflicted>
+```
+
 </structured_returns>
 
 <success_criteria>