work with fusion's sidekick; reject fusion-* role slugs

docs/guide/01-setup.md

@@ -28,6 +28,8 @@ You only override what you care about. A role with no line in the rule keeps the
 
 You might be wondering what happens on Adaptive. Set a role to `inherit-parent` or `auto` and pstack spawns that role's subagents with `subagent_general` or `subagent_explore`, so they follow your parent chat model. Both values mean the same thing, and neither is a model slug. For a panel role the value is a list, and one subagent runs per entry, so the list length sets the panel size. Setup also configures `swarm workers`, the default model for every `/pstack:swarm` worker unless a race names a model for each arm.
 
+On Fusion, pstack shares the work with the sidekick. A step that hands one agent hands-on work, like writing the code or running a check, goes to the sidekick. It runs on the sidekick model you picked in `/fusion`, not on that step's role line. Panels, fan-out, and second opinions still run as pstack subagents on the models in your rule. A role set to `auto` or `inherit-parent` can run on the lead model, at the lead's price. Chats without Fusion work as described above.
+
 ## Accept the verification offers, or don't
 
 At the end of setup, `/pstack:setup-pstack` looks for a way to prove app behavior in your project, either a `verify-*` skill or an existing harness. If it finds neither, it offers once to generate one with [`/pstack:create-verification-skill`](../../skills/create-verification-skill/SKILL.md).
@@ -45,7 +47,7 @@ After setup, start a new chat. The model rule applies to new sessions.
 pstack spends extra tokens on subagents and review panels. That's the price of the rigor. To spend fewer:
 
 - Rerun `/pstack:setup-pstack` and pick a smaller reasoning budget or cheaper models. A strong model in the main chat with cheaper, faster models in the code roles is a good split.
-- Set a role to `auto` or `inherit-parent` so it runs on the chat's own model.
+- Set a role to `auto` or `inherit-parent` so it runs on the chat's own model. On Fusion that can be the lead, so pin the sidekick's slug instead.
 - Shorten a panel list. Each entry runs one subagent.
 - Save `/pstack:poteto-mode` for work that needs rigor. A small, obvious edit doesn't.
 

docs/guide/10-recipes-and-pitfalls.md

@@ -172,6 +172,7 @@ That's the whole prompt. [`/pstack:bro`](../../skills/bro/SKILL.md) restates the
 - **Using `/pstack:arena` for coverage.** `/pstack:arena` repeats one design or code brief, then picks a base and grafts the best parts. `/pstack:swarm` partitions slices or declared race arms and aggregates one report.
 - **Accepting every review comment.** Bots and humans both file real catches and noise in one list. `/pstack:interrogate` sorts findings into act-on and dismissed buckets with reasons, and you can override either way.
 - **Treating `auto` as a model slug.** `auto` and `inherit-parent` mean "omit the model field so the subagent inherits the parent chat model." [Setup](./01-setup.md) covers the roles.
+- **Putting a Fusion model in a role.** A `fusion-*` slug names a lead and sidekick pair for the main chat, so pstack rejects it and falls back to the role's default. Pick the lead's or the sidekick's own slug, like `claude-opus-5-5-max` or `swe-2-high`.
 - **Reporting success off a green build.** A build proves it compiles. Ask for the real command, flow, stored value, or profile, and expect the evidence in the reply.
 - **Writing a `SKILL.md` freehand.** Route it through the [Authoring or modifying a skill playbook](../../skills/poteto-mode/playbooks/authoring-a-skill.md) so validation and review happen.
 

skills/arena/SKILL.md

@@ -14,7 +14,7 @@ Every candidate gets the same prompt, so the prompt is the contract.
 
 1. State the artifact each candidate is producing.
 2. Derive the rubric, 3-6 concrete gradeable criteria for what success looks like on *this* task. It is the picker's tool in Phase D. Candidates only see the task.
-3. Pick the runners. Use the `arena runners` line in `~/.devin/rules/pstack-models.md`. If the rule or that line is missing, default to one each on `claude-opus-5-5-xhigh` and `swe-2-high`. Map each entry to the spawn's `profile`: a real slug `M` becomes `pstack-M`, and `auto` or `inherit-parent` means the parent model, so use `subagent_general` for it. Create a missing `pstack-M` profile per `/pstack:setup-pstack`. An entry `devin models list` doesn't report counts as a rejected slug; never create a profile for it. If a pinned slug is rejected at spawn, run that seat on its family's default and say so. Families go by prefix: `claude-*`, `gpt-*`, `swe-*`, `gemini-*`, plus the short aliases (`opus`, `sonnet`, `swe`, `codex`, `gpt`, `gemini`). With no family match, use `claude-opus-5-5-xhigh`. If it rejects a default, use the closest valid slug of the same family `devin models list` reports. Spawn more runners when the arena covers multiple design directions. Use the same model N times when the work is generation-bound rather than judgment-sensitive. Pick each subagent's reasoning level and fast or standard speed for the job, per the Subagents section of the **poteto-mode** skill.
+3. Pick the runners. Use the `arena runners` line in `~/.devin/rules/pstack-models.md`. If the rule or that line is missing, default to one each on `claude-opus-5-5-xhigh` and `swe-2-high`. Map each entry to the spawn's `profile`: a real slug `M` becomes `pstack-M`, and `auto` or `inherit-parent` means the parent model, so use `subagent_general` for it. Create a missing `pstack-M` profile per `/pstack:setup-pstack`. An entry `devin models list` doesn't report, or any `fusion-*` entry, counts as a rejected slug; never create a profile for it. If a pinned slug is rejected at spawn, run that seat on its family's default and say so. Families go by prefix: `claude-*`, `gpt-*`, `swe-*`, `gemini-*`, plus the short aliases (`opus`, `sonnet`, `swe`, `codex`, `gpt`, `gemini`). With no family match, use `claude-opus-5-5-xhigh`. If it rejects a default, use the closest valid slug of the same family `devin models list` reports. Spawn more runners when the arena covers multiple design directions. Use the same model N times when the work is generation-bound rather than judgment-sensitive. Pick each subagent's reasoning level and fast or standard speed for the job, per the Subagents section of the **poteto-mode** skill.
 4. Give each candidate its own output location (a git worktree where possible, otherwise `/tmp/arena-<slug>/candidate-<n>/`), per the **separate-before-serializing-shared-state** principle skill.
 
 ## Phase B: Fan out
@@ -25,7 +25,7 @@ If a candidate produces no output, proceed with N-1 and note the dropout.
 
 ## Phase C: Cross-judge
 
-After all Phase B candidates complete, choose one model from the `arena cross-judge pool` line in `~/.devin/rules/pstack-models.md`. If the rule or that line is missing, choose from `claude-opus-5-5-xhigh` and `swe-2-high`. Prefer a different model family from the parent's. Spawn one read-only judge subagent on it (`pstack-M-ro`, or `subagent_explore` for `auto`/`inherit-parent`). An entry `devin models list` doesn't report counts as a rejected slug; never create a profile for it. It sees the rubric and the candidates by path label, scores each criterion, and recommends a base with rationale. It runs in parallel with your reading in Phase D. Don't spawn it while candidates are still writing.
+After all Phase B candidates complete, choose one model from the `arena cross-judge pool` line in `~/.devin/rules/pstack-models.md`. If the rule or that line is missing, choose from `claude-opus-5-5-xhigh` and `swe-2-high`. Prefer a different model family from the parent's. On Fusion, prefer one outside both the lead's and the sidekick's families, else outside the lead's. Spawn one read-only judge subagent on it (`pstack-M-ro`, or `subagent_explore` for `auto`/`inherit-parent`). An entry `devin models list` doesn't report, or any `fusion-*` entry, counts as a rejected slug; never create a profile for it. It sees the rubric and the candidates by path label, scores each criterion, and recommends a base with rationale. It runs in parallel with your reading in Phase D. Don't spawn it while candidates are still writing.
 
 ## Phase D: Pick a base
 

skills/how/SKILL.md

@@ -8,7 +8,7 @@ triggers: [user]
 
 Explore the codebase to answer "how does X work?" questions. Produce architectural explanations at the level of a senior engineer onboarding onto a subsystem, enough to build a working mental model, not so much that it reads like annotated source code.
 
-Every spawn is a read-only `run_subagent` subagent. Explorers use the `how explorer` line in the `pstack-models.md` rule (default `swe-2-high`), and every explainer uses the `how explainer` line (default `claude-opus-5-5-xhigh`). Map each role's value to the spawn's `profile`: a real slug `M` becomes `pstack-M-ro`; `auto`, `inherit-parent`, or a missing rule or line uses `subagent_explore`, or `subagent_general` with a read-only brief when the explorer needs `exec` or MCP. Create a missing `pstack-M-ro` profile per `/pstack:setup-pstack` rather than swapping models. An entry `devin models list` doesn't report counts as a rejected slug; never create a profile for it. Pick each subagent's reasoning level and fast or standard speed for the job, per the Subagents section of the **poteto-mode** skill.
+Every spawn is a read-only `run_subagent` subagent. Explorers use the `how explorer` line in the `pstack-models.md` rule (default `swe-2-high`), and every explainer uses the `how explainer` line (default `claude-opus-5-5-xhigh`). Map each role's value to the spawn's `profile`: a real slug `M` becomes `pstack-M-ro`; `auto`, `inherit-parent`, or a missing rule or line uses `subagent_explore`, or `subagent_general` with a read-only brief when the explorer needs `exec` or MCP. Create a missing `pstack-M-ro` profile per `/pstack:setup-pstack` rather than swapping models. An entry `devin models list` doesn't report, or any `fusion-*` entry, counts as a rejected slug; never create a profile for it. Pick each subagent's reasoning level and fast or standard speed for the job, per the Subagents section of the **poteto-mode** skill.
 
 ## 1. Assess complexity
 

skills/interrogate/SKILL.md

@@ -31,7 +31,7 @@ Launch all reviewers in a single message with run_subagent, one per entry on the
 | Reviewer A | `claude-opus-5-5-xhigh` |
 | Reviewer B | `swe-2-high` |
 
-Each reviewer is read-only and gets `profile` from its configured entry, or its table default when there is no configured line. A real slug `M` becomes `pstack-M-ro` (create it per `/pstack:setup-pstack` if missing). An entry `devin models list` doesn't report counts as a rejected slug; never create a profile for it. An `auto` or `inherit-parent` entry uses `subagent_explore`, so that reviewer runs on the parent-assigned default; use `subagent_general` with a read-only brief when the review needs `exec` or MCP.
+Each reviewer is read-only and gets `profile` from its configured entry, or its table default when there is no configured line. A real slug `M` becomes `pstack-M-ro` (create it per `/pstack:setup-pstack` if missing). An entry `devin models list` doesn't report, or any `fusion-*` entry, counts as a rejected slug; never create a profile for it. An `auto` or `inherit-parent` entry uses `subagent_explore`, so that reviewer runs on the parent-assigned default; use `subagent_general` with a read-only brief when the review needs `exec` or MCP.
 
 If a pinned slug is rejected at spawn, run that reviewer on its family's table default and say so. Families go by prefix: `claude-*`, `gpt-*`, `swe-*`, `gemini-*`, plus the short aliases (`opus`, `sonnet`, `swe`, `codex`, `gpt`, `gemini`). With no family match, use Reviewer A's default. If it rejects a table default, spawn with the closest equivalent `devin models list` reports (prefer the same family and reasoning tier), and open a separate PR to update the default table. Do not block the review on the slug issue. Never treat an alias entry as a rejected slug or apply either fallback to it.
 

skills/poteto-help/SKILL.md

@@ -41,9 +41,9 @@ When the model rule is missing and it matters, ask whether the user wants to pic
 
 Installing changes nothing until the user invokes a skill. Only `/pstack:setup-pstack` loads from the user's words. The [README](../../README.md) and [guide page 1](../../docs/guide/01-setup.md) have the details. Offer to word their first prompt with them, per [`references/prompting.md`](references/prompting.md).
 
-If cost is the worry, say where the tokens go and how to spend fewer. pstack spends extra tokens on subagents and review panels. Rerun `/pstack:setup-pstack` and pick a smaller budget or cheaper models. A role set to `auto` or `inherit-parent` runs on the chat's model, which saves tokens when the chat runs on Auto or a cheaper model. A shorter panel list runs fewer subagents, one for each entry. Save `/pstack:poteto-mode` for work that needs rigor.
+If cost is the worry, say where the tokens go and how to spend fewer. pstack spends extra tokens on subagents and review panels. Rerun `/pstack:setup-pstack` and pick a smaller budget or cheaper models. A role set to `auto` or `inherit-parent` runs on the chat's model, which saves tokens when the chat runs on Auto or a cheaper model. On Fusion it can run on the lead model, so pinning the sidekick's slug costs less. A shorter panel list runs fewer subagents, one for each entry. Save `/pstack:poteto-mode` for work that needs rigor.
 
-This is the Devin port of pstack. Its skills use the Agent Skills format, its subagents run on Devin's `run_subagent`, and per-role models work through the `pstack-<slug>` profiles `/pstack:setup-pstack` writes.
+This is the Devin port of pstack. Its skills use the Agent Skills format, its subagents run on Devin's `run_subagent`, and per-role models work through the `pstack-<slug>` profiles `/pstack:setup-pstack` writes. On Fusion, a step that hands one agent hands-on work goes to the sidekick, and panels and fan-out stay on `run_subagent`.
 
 ## Start a task with `/pstack:poteto-mode`