fix: harden orchestration and qualify Fable 5.1

[CBEPX]

Summary

• classify the benign Client.listTools() capability warning as a bounded stable diagnostic without weakening unknown-parser fail-closed behavior
• preserve allowlisted peer validation details through workflow state, Codex/Claude retries, reservation rotation, rendering, and tracked errors
• make checkpoint waiting one-shot and terminal-aware while preserving aggregate failure across late sibling races and allowing real recovery
• let authoritative runner results atomically replace status-reaper guesses without overwriting cancellation or unrelated terminal writers
• qualify the floating fable alias and pinned claude-fable-5-1 telemetry for Fable 5.1, and prepare release metadata for 1.7.1
• keep MCP clientInfo release versions under the existing version-sync gate

Verification

• npm run check: 924 unit, 104 integration, 23 E2E tests passed
• npm run test:coverage: 1051/1051 passed; 92.6% statements, 83.37% branches, 98.26% functions
• state mutation dry-run: 2 files, 904 mutants instrumented, baseline passed
• npm pack --dry-run: 89 files, no tests or SDD artifacts
• independent whole-branch Codex review plus scoped re-review: approved after the final fix wave
• Claude Code adversarial review through cc with pinned claude-fable-5-1/high identified the final retry/reaper gaps addressed here

Proof boundary

This PR establishes source and local-test readiness. Publication, exact-tag activation, and post-restart live model/workflow smoke are separate gates after merge.

Closes #18
Closes #21
Closes #22
Closes #23