fix(quorum): backport CLI fallback to probe-quorum-slots

[jobordu]

Summary

• Backport PR fix(quorum): resolve CLI from mainTool when cli is null (call-quorum-slot) #164's `resolvedCli || cli || mainTool` fallback chain to `bin/probe-quorum-slots.cjs` so it no longer crashes with `spawn: file argument must be of type string. Received null` when invoked.
• Backport PR fix(quorum): prefer slash-path providers.json so Daintree slots are visible #165's `findProviders()` skip-empty + canonical-first ordering so the repo's empty `bin/providers.json` skeleton doesn't short-circuit the search before the installed providers.json is found.

Why

`provider.cli` is null for all 5 sub slots (codex-1, gemini-1, opencode-1, copilot-1, claude-1) in the canonical `~/.claude/nf/bin/providers.json`. The hot path (`call-quorum-slot.cjs`) handles this via the three-tier fallback added in #164, but the diagnostic probe script was missing the same fix. Calling it directly would crash before reaching any slot.

Surfaced by a `/nf:quorum` self-test run where codex-1 caught the gap (cited `bin/probe-quorum-slots.cjs:27,67`). Quorum reached consensus that the hot-path was fine but the probe tool needed the same backport.

Test plan

• `node bin/probe-quorum-slots.cjs --slots codex-1,gemini-1,opencode-1,copilot-1,claude-1 --timeout 8000` returns valid JSON (3 healthy, 2 timeouts at 8s — gemini-1 and claude-1 are real LLM calls; not a regression).
• `npm run lint:isolation` → passes
• `node --test test/quorum-preflight-probe.test.cjs` → 9/9 pass
• CI: run full `test:ci` suite

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Graceful failure when no executable can be resolved for a provider—slots now report failures instead of attempting to spawn invalid commands.
  • Robust provider-file loading: skips empty provider lists and continues on parse/read errors.

• Improvements

  • Expanded automatic discovery paths for provider configuration files.
  • Caches resolved executables and improves fallback logic when CLI specs are missing.

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Walkthrough

bin/probe-quorum-slots.cjs now expands provider file discovery paths to include ~/.claude locations, improves provider file loading with existence checks and empty-provider-list handling, and implements CLI resolution for subprocess providers using resolveCli to derive spawn targets from provider.mainTool when provider.cli is omitted.

Changes

Quorum slot probing with CLI resolution

Layer / File(s)	Summary
Provider file discovery and loading bin/probe-quorum-slots.cjs	Adds resolveCli import, extends findProviders() search paths to include additional ~/.claude locations, and updates provider-file loading to check existence first, parse { providers }, skip empty provider arrays, and continue on errors.
CLI resolution for subprocess probing bin/probe-quorum-slots.cjs	In probeSlot(), treats provider.cli as optional, derives provider.resolvedCli from provider.mainTool via resolveCli when needed, selects a non-empty spawn target, and returns a structured failure result when no resolvable spawn target exists; uses spawnTarget for the spawn call.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• nForma-AI/nForma#161: Implements the same resolveCli fallback pattern for subprocess CLI resolution in unified-mcp-server.mjs to avoid null spawn targets.
• nForma-AI/nForma#165: Updates provider discovery to prefer ~/.claude/nf/bin/providers.json and improves loading to skip empty/missing provider lists.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: backporting CLI fallback logic to the probe-quorum-slots script to fix null reference crashes.
Description check	✅ Passed	The description covers what was changed, why it was needed, and includes test results, following the template's core requirements even though not all checkbox items are completed.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Commit unit tests in branch fix/probe-quorum-slots-cli-fallback

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[jobordu]

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

bin/probe-quorum-slots.cjs (1)

35-38: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Keep the canonical providers file first.

Line 38 prepends path.dirname(serverScript)/providers.json, so a non-empty sibling file can still override ~/.claude/nf/bin/providers.json. That undermines the canonical-first lookup this backport is trying to restore and can make the probe read a stale repo/local config instead of the live quorum config.

Suggested fix

   try {
     const claudeJson = JSON.parse(fs.readFileSync(path.join(os.homedir(), '.claude.json'), 'utf8'));
     const u1args = claudeJson?.mcpServers?.['unified-1']?.args ?? [];
     const serverScript = u1args.find(a => typeof a === 'string' && a.endsWith('unified-mcp-server.mjs'));
-    if (serverScript) searchPaths.unshift(path.join(path.dirname(serverScript), 'providers.json'));
+    if (serverScript) {
+      const siblingProviders = path.join(path.dirname(serverScript), 'providers.json');
+      if (!searchPaths.includes(siblingProviders)) searchPaths.splice(1, 0, siblingProviders);
+    }
   } catch (_) {}

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@bin/probe-quorum-slots.cjs` around lines 35 - 38, The code currently prepends
the sibling providers.json (found via serverScript) into searchPaths which
allows that file to override the canonical ~/.claude/nf/bin/providers.json;
change the logic so the sibling providers.json is appended (use
searchPaths.push(path.join(path.dirname(serverScript), 'providers.json')) or
otherwise insert it after the canonical entry) so the canonical providers file
remains first; update the block that reads claudeJson, computes u1args and
serverScript and replace the unshift call on searchPaths with a push (or
equivalent insertion after the canonical path) to preserve canonical-first
lookup.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@bin/probe-quorum-slots.cjs`:
- Around line 35-38: The code currently prepends the sibling providers.json
(found via serverScript) into searchPaths which allows that file to override the
canonical ~/.claude/nf/bin/providers.json; change the logic so the sibling
providers.json is appended (use
searchPaths.push(path.join(path.dirname(serverScript), 'providers.json')) or
otherwise insert it after the canonical entry) so the canonical providers file
remains first; update the block that reads claudeJson, computes u1args and
serverScript and replace the unshift call on searchPaths with a push (or
equivalent insertion after the canonical path) to preserve canonical-first
lookup.

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• bin/probe-quorum-slots.cjs