fix(mode): prepend the assemble filter; structured_output joins the plan allowlist
Review finding with a real in-repo instance: the structured runtime's per-spawn final-assembly wrapper (prepend, post-next) re-injects structured_output OUTSIDE the mode filter, so a structured child in plan mode would see a tool the gate then denies — the soft policy and the hard gate telling different stories. The suggested fix (make the mode filter outermost) cannot beat that instance: prepend unshifts, so the per-spawn listener always registers later and wraps outer. Two-part resolution instead. Semantically, structured_output enters the shipped plan allowlist — it is a child's pure result channel, the same ask/report class as ask_user_question and exit_plan_mode, so the filter, the re-injection, and the gate now agree wherever a structured child runs in plan mode. Mechanically, the filter registers with prepend anyway: it now wraps outside every append-registered listener regardless of load order (regression test pins a pre-registered post-next mutator being filtered), narrowing the documented cosmetic residual to prepend-after-load listeners only, where the gate still covers execution. Severity note: no execution breach existed — the gate held throughout; this closes the prompt-honesty gap.
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@@ -159,7 +159,7 @@ set(agent: Agent, mode: string): void
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Types: [Agent](../core-data-structures/core.md)
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Source: [`packages/mode/mode/src/index.ts:205`](../../packages/mode/mode/src/index.ts)
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Source: [`packages/mode/mode/src/index.ts:210`](../../packages/mode/mode/src/index.ts)
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## `ctx.sessionPersistence` — `SessionPersistence` (abstract seam)
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@@ -43,10 +43,10 @@ Mode definitions are validated plugin Config — per repo convention, changeable
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section: |
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You are in plan mode: explore and design, then present the
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plan for approval through exit_plan_mode.
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tools: [read, todo_write, web_search, web_fetch, ask_user_question, exit_plan_mode]
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tools: [read, todo_write, web_search, web_fetch, ask_user_question, structured_output, exit_plan_mode]
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```
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`plan`'s shipped default allowlist is the read-only surface (`read`, `todo_write`, `web_search`/`web_fetch`, `ask_user_question`, `exit_plan_mode`) with `bash` and `subagent` excluded until the sandbox family can actually confine them — a deployment that accepts the risk widens its own config today. `default` is reserved (the absence of policy) and rejected as a key; an unknown mode name fails validation loudly at `set()` time.
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`plan`'s shipped default allowlist is the read-only surface (`read`, `todo_write`, `web_search`/`web_fetch`, `ask_user_question`, `structured_output`, `exit_plan_mode` — the last three are the pure ask/report class) with `bash` and `subagent` excluded until the sandbox family can actually confine them — a deployment that accepts the risk widens its own config today. `default` is reserved (the absence of policy) and rejected as a key; an unknown mode name fails validation loudly at `set()` time.
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### In the terminal
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@@ -94,7 +94,7 @@ A contained `session/event` listener ([defensive patterns](../../../defensive-pa
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A `system-prompt/assemble` waterfall listener reads the calling agent's mode (the `AssembleContext` carries `agent`) and, in a non-default mode, filters `assembly.tools` down to the mode's allowlist and appends the mode's guidance section. The loop already renders per step and logs the result: entering or leaving a mode surfaces on the next step as a `request/header-delta` — or as the full `request/header` fallback snapshot when the change is inexpressible in the delta encoding (adding `exit_plan_mode` resorts the canonical tool list, and a pure reordering has no delta form) — so every mode transition is an attributable log fact. The section is static per mode and the plan itself stays in the conversation (messages and tool args, already in context), so a mode does not add per-step prompt churn — re-injecting plan state into every request ([Prior art](#prior-art)'s compaction-survival hack) is unnecessary and would only burn prefix cache.
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The guidance section is an ordinary registered section, `{ name: 'mode:policy', order: 50, text: context => … }` — order 50 sits after the persona (0) and before tool guidance (100–199); it resolves to the folded mode's configured text and to `''` (dropped at render) for the default mode or an agent-less assembly. The tool filter wraps: it awaits `next()` and filters the RETURNED assembly's `tools`, so additions made anywhere inside its wrap are covered. The filter enforces one rule in every mode: `exit_plan_mode` is visible IFF the agent's folded mode is `plan` — which is also what keeps a default-mode assembly byte-identical to a no-`dsh-mode` deployment even though the tool is always registered. In a non-default mode it additionally intersects with the mode's allowlist.
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The guidance section is an ordinary registered section, `{ name: 'mode:policy', order: 50, text: context => … }` — order 50 sits after the persona (0) and before tool guidance (100–199); it resolves to the folded mode's configured text and to `''` (dropped at render) for the default mode or an agent-less assembly. The tool filter wraps with `prepend: true`: it awaits `next()` and filters the RETURNED assembly's `tools`, so additions made anywhere inside its wrap — including every append-registered listener's post-`next()` mutation, regardless of load order — are covered. The filter enforces one rule in every mode: `exit_plan_mode` is visible IFF the agent's folded mode is `plan` — which is also what keeps a default-mode assembly byte-identical to a no-`dsh-mode` deployment even though the tool is always registered. In a non-default mode it additionally intersects with the mode's allowlist.
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### The hard layer: the gate
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@@ -193,4 +193,4 @@ What holds now, pinned by the unit, protocol, and snapshot tiers:
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- `exit_plan_mode`'s approve path flips the mode and restores the full toolset on the next step; the keep-planning path returns the corrective `isError` carrying the user's feedback and stays in plan mode; the ACP `session/set_mode` round-trip updates `current_mode_update`, and the exit review prompts through each surface's user-interaction provider.
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- The docs tail shipped with the landing: READMEs, regenerated catalogs (persistence log, config, cordis services, tools), the packages map and architecture rows, and the cookbook row.
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The accepted costs: a pending user flip set while idle is lost if the process dies before the next turn (the UI re-applies; the idle-record primitive is the escape hatch if this bites in practice). Every mode transition is a logged header change and therefore a prefix-cache reset at the provider — inherent, visible in per-step usage, and an argument against mode-flapping UIs, not against the design. Sibling-listener order is not deterministic, so a foreign assemble listener wrapping OUTSIDE the mode listener could re-widen filtered schemas — the filter runs on the assembly `next()` returns, and the hard gate keeps anything re-widened non-executable; the residual cost is cosmetic (the model sees a tool it cannot use), accepted rather than mechanized. Plan mode's shipped allowlist excludes `bash` and `subagent`, which costs real exploration power until the sandbox family and mode inheritance land — a deployment that accepts the risk can widen its own config today. Two in-flight stacks touch the ACP mode surface (this one and the sandbox branch's config options, whose feature-matrix stance records session modes as deliberately unmodeled): the picker-to-modes / knobs-to-config-options division pinned in the [FAQ](#faq) is the contract, and the sandbox branch owes its matrix rows an amendment on merge-down. The ACP spec's draft v2 direction reportedly slates session modes for removal in favor of config options; if that lands, the picker migrates to a config-option select mechanically — the mode state and both enforcement layers are wire-agnostic — accepted.
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The accepted costs: a pending user flip set while idle is lost if the process dies before the next turn (the UI re-applies; the idle-record primitive is the escape hatch if this bites in practice). Every mode transition is a logged header change and therefore a prefix-cache reset at the provider — inherent, visible in per-step usage, and an argument against mode-flapping UIs, not against the design. The mode filter prepends, so only a listener that ALSO prepends after `dsh-mode` loads can wrap outside it and re-widen filtered schemas — the one shipped instance is the structured runtime's per-spawn final-assembly wrapper, whose `structured_output` is on the plan allowlist precisely so the filter, that wrapper, and the gate agree; for any future such listener the hard gate keeps a re-widened tool non-executable, and the residual cost is cosmetic (the model sees a tool it cannot use), accepted rather than mechanized. Plan mode's shipped allowlist excludes `bash` and `subagent`, which costs real exploration power until the sandbox family and mode inheritance land — a deployment that accepts the risk can widen its own config today. Two in-flight stacks touch the ACP mode surface (this one and the sandbox branch's config options, whose feature-matrix stance records session modes as deliberately unmodeled): the picker-to-modes / knobs-to-config-options division pinned in the [FAQ](#faq) is the contract, and the sandbox branch owes its matrix rows an amendment on merge-down. The ACP spec's draft v2 direction reportedly slates session modes for removal in favor of config options; if that lands, the picker migrates to a config-option select mechanically — the mode state and both enforcement layers are wire-agnostic — accepted.
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