feat(setup): flex dispatch matrix, assignment-first setup, and lane docs

[thisguymartin]

Closes #4

Builds on the gateway runner merged in #1. This PR adds routing, setup, and docs.

What changed

• Adds the DeepSeek deepseek-flash and MiniMax MiniMax-M3 flex model rows. Both route through the external runner under Claude Code and Codex. A reported model mismatch fails; a missing report is marked unverified.
• Changes setup to assign roles first, then ask effort and probe only assigned families. This permits a DeepSeek and MiniMax-only configuration while preserving the stock model matrix.
• Adds the lane guide, usage guide, safety notes, and fork documentation. The guides now describe the runner's actual environment isolation and model receipt behavior.

OpenCode parent support from the legacy repository is outside this PR.

Verification

• Bun tests, strict typecheck, static invariants, and plugin validation pass.
• The exact candidate is installed in every affected harness.
• The changed behavior passes from each real user surface.
• The installed version, action, and observed result appear below.

Local gate on 92dc0bc: 187 Bun tests pass; strict typecheck, manifest parsing, static invariants, and claude plugin validate plugins/pstack pass. Relative links in the changed guides resolve.

Live evidence:

• MiniMax source-runner probe passed at 92dc0bc from the Codex terminal using Claude Code 2.1.283, an isolated config directory, and a synthetic prompt. --provider minimax --model MiniMax-M3 --effort high --mode read-only exited 0 and returned PSTACK_MINIMAX_OK. Receipt: status: complete, reportedModel: MiniMax-M3, modelVerified: true, modelEvidence: provider-report, costUsd: null. The temporary Claude config was removed. This tests the source runner; the installed-plugin and setup-flow gate remains open.

• DeepSeek source-runner probe passed at 92dc0bc from the Codex terminal using Claude Code 2.1.283, an isolated config directory, and a synthetic prompt. --provider deepseek --model deepseek-flash --effort high --mode read-only exited 0 and returned PSTACK_DEEPSEEK_OK. Receipt: status: complete, reportedModel: deepseek-flash, modelVerified: true, modelEvidence: provider-report, costUsd: null. The temporary Claude config was removed. This tests the source runner; it does not satisfy the installed-plugin or setup-flow gate.

Installed setup tests

Tested candidate 92dc0bcbb794398c7216d626310f2e146fbfcb07, plugin version 1.4.1, on 2026-09-28 UTC. An independent byte comparison confirmed all 168 tracked plugin files match the candidate in both test loads, before merge.

User interface	Exact candidate load	Action	Observed result
Codex CLI 0.157.1, parent gpt-6-astra	Installed pstack@pstack-pr2-live from a temporary local marketplace into the Codex plugin cache	Invoke $setup-pstack; assign only DeepSeek and MiniMax at high; save the sheet; run both probes, both panel lanes, and a MiniMax cross-judge of the DeepSeek candidate	5/5 external runs complete, exit 0, expected markers, matching provider-reported models; cross-judge returns PASS
Claude Code CLI 2.1.283	Session-load the exact archived plugin through --plugin-dir	Invoke /pstack:setup-pstack; same two-family assignments; run both probes, both panel lanes, and each provider judging the other candidate	6/6 external runs complete, exit 0, expected markers, matching provider-reported models; both cross-judges return PASS

Both sessions used synthetic data and redirected only the model-sheet and integration destinations to temporary files. This exercised the installed setup instructions without changing the user's active model choices. All 15 role rows matched the requested assignments; Arena and Interrogate retained two-provider diversity; Why and Reflect remained inherit-parent. No unassigned family was probed. Codex mirrored the exact sheet bytes inside one bounded block. Claude added one include for its test sheet. Both preserved the existing integration content.

Independent inspection of all 11 receipts and output files confirmed the actual parent, read-only mode, high requested effort, deepseek-flash or MiniMax-M3 as appropriate, modelVerified: true, modelEvidence: provider-report, and costUsd: null. This does not claim observability of hidden applied reasoning depth or test the user's permanent configuration paths. All processes were drained and temporary gateway config directories removed.

Local evidence: /tmp/pstack-pr2-installed-evidence.json contains receipt paths and SHA-256 hashes. Complete CLI transcripts, prompts, sheets, integration snapshots, and outputs are retained in the temporary pstack-codex-setup-ck14awo7 and pstack-claude-setup-87sptmwr test directories. Credentials were supplied through process environment and excluded from evidence.

GitHub reports no registered CI checks for this fork. The local verification listed above and the installed behavioral tests passed on the exact candidate.