fix: delete AskUserQuestion fallback (root cause of forever war)

The /plan-eng-review skill failed to fire AskUserQuestion on a real
plan review and surfaced 4 calibration decisions via prose instead.
Investigation traced this to a "fallback when neither variant is
callable" clause in the preamble that the model rationalizes around
as a general escape hatch from "fanning out round-trip AUQs," even
when an AUQ variant IS callable. Codex review confirmed the fallback
exists in 8 inline sites with 2 surviving escape hatches the original
narrowing missed (a "genuinely trivial" exception duplicated across
all 4 plan-* templates, and a "outside plan mode, output as prose
and stop" branch in the preamble itself).

Net deletion in skill text. Closes both branches of the deleted
fallback (plan-file write AND prose-and-stop) and the trivial-fix
exception with a single hard rule:

  If no AskUserQuestion variant appears in your tool list, this
  skill is BLOCKED. Stop, report `BLOCKED — AskUserQuestion
  unavailable`, and wait for the user.

Honest about being a model directive, not a runtime guard — none of
the PTY harness helpers enforce BLOCKED today. The architectural
improvement is that the model has fewer alternatives to obey it
against. Runtime enforcement is a follow-up TODO.

Sources changed:
- scripts/resolvers/preamble/generate-ask-user-format.ts: delete both
  fallback branches; replace with 1-line BLOCKED rule
- scripts/resolvers/preamble/generate-completion-status.ts: delete
  fallback in generatePlanModeInfo
- plan-eng-review/SKILL.md.tmpl: delete fallback at Step 0 + Sections
  1-4 (5 instances) + delete trivial-fix exception
- office-hours/SKILL.md.tmpl: delete fallback in approach-selection
- plan-ceo-review/SKILL.md.tmpl: delete trivial-fix exception
- plan-design-review/SKILL.md.tmpl: delete trivial-fix exception
- plan-devex-review/SKILL.md.tmpl: delete trivial-fix exception

Generated SKILL.md regen lands in a follow-up commit per the bisect
convention (template changes separate from regenerated output).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/resolvers/preamble/generate-ask-user-format.ts

@@ -9,7 +9,7 @@ export function generateAskUserFormat(_ctx: TemplateContext): string {
 
 **Rule:** if any \`mcp__*__AskUserQuestion\` variant is in your tool list, prefer it. Hosts may disable native AUQ via \`--disallowedTools AskUserQuestion\` (Conductor does, by default) and route through their MCP variant; calling native there silently fails. Same questions/options shape; same decision-brief format applies.
 
-**Fallback when neither variant is callable:** in plan mode, write the decision brief into the plan file as a \`## Decisions to confirm\` section + ExitPlanMode (the native "Ready to execute?" surfaces it). Outside plan mode, output the brief as prose and stop. **Never silently auto-decide** — only \`/plan-tune\` AUTO_DECIDE opt-ins authorize auto-picking.
+**If no AskUserQuestion variant appears in your tool list, this skill is BLOCKED.** Stop, report \`BLOCKED — AskUserQuestion unavailable\`, and wait for the user. Do not write decisions to the plan file as a substitute, do not emit them as prose and stop, and do not silently auto-decide (only \`/plan-tune\` AUTO_DECIDE opt-ins authorize auto-picking).
 
 ### Format
 

scripts/resolvers/preamble/generate-completion-status.ts

@@ -26,7 +26,7 @@ In plan mode, allowed because they inform the plan: \`$B\`, \`$D\`, \`codex exec
 
 ## Skill Invocation During Plan Mode
 
-If the user invokes a skill in plan mode, the skill takes precedence over generic plan mode behavior. **Treat the skill file as executable instructions, not reference.** Follow it step by step starting from Step 0; the first AskUserQuestion is the workflow entering plan mode, not a violation of it. AskUserQuestion (any variant — \`mcp__*__AskUserQuestion\` or native; see "AskUserQuestion Format → Tool resolution") satisfies plan mode's end-of-turn requirement. If no variant is callable, fall back to writing the decision brief into the plan file as a \`## Decisions to confirm\` section + ExitPlanMode — never silently auto-decide. At a STOP point, stop immediately. Do not continue the workflow or call ExitPlanMode there. Commands marked "PLAN MODE EXCEPTION — ALWAYS RUN" execute. Call ExitPlanMode only after the skill workflow completes, or if the user tells you to cancel the skill or leave plan mode.`;
+If the user invokes a skill in plan mode, the skill takes precedence over generic plan mode behavior. **Treat the skill file as executable instructions, not reference.** Follow it step by step starting from Step 0; the first AskUserQuestion is the workflow entering plan mode, not a violation of it. AskUserQuestion (any variant — \`mcp__*__AskUserQuestion\` or native; see "AskUserQuestion Format → Tool resolution") satisfies plan mode's end-of-turn requirement. If no variant is callable, the skill is BLOCKED — stop and report \`BLOCKED — AskUserQuestion unavailable\` per the AskUserQuestion Format rule. At a STOP point, stop immediately. Do not continue the workflow or call ExitPlanMode there. Commands marked "PLAN MODE EXCEPTION — ALWAYS RUN" execute. Call ExitPlanMode only after the skill workflow completes, or if the user tells you to cancel the skill or leave plan mode.`;
 }
 
 export function generateCompletionStatus(ctx: TemplateContext): string {