feat(subagent): enforce one recovery per failure via spawn_agent

The single-successor hint for a transient worker failure was advisory:
nothing tied a successor to the failed run, counted it, or stopped a
second one. spawn_agent now takes recovers, the failed agent id. The
claim is recorded synchronously before the handler awaits, so duplicate
or concurrent calls get the same replacement back and spawn nothing; an
ineligible request is refused with its typed reason and never falls
back to a plain spawn. A replacement is attempt 2, so its own failure
is recovery_exhausted, and it is an ordinary spawn that inherits no
grants, approvals, or pending asks. Reverting this restores the
advisory guidance.

Author: bwachman

docs/ARCHITECTURE.md

@@ -153,7 +153,7 @@ Two directors, selected by role:
   Auto mode is toggled by CLI flags (`--auto` / `--no-auto`); there is currently no in-session key to toggle it (default on; constrained envelope — workspace writes and unconstrained shell auto-allow; installs, recursive rm, force/uncontained worktree changes, sensitive-path and opaque-wrapper shell still ask; contained non-force `git worktree add`/`remove`/`prune` and `list` auto-allow; shell file-mutation denied). It is not a separate edit/plan mode.
 
 - **SubAgentDirector** (delegated work, `src/subagent/index.ts`) — Drives a dispatched worker until a turn arrives with no tool calls, then replies with the final assistant text and ends the run. A tool-less turn **after tools** completes only with the four-heading envelope (Summary, Findings, Blockers, Paths). Assistant text that prints explicit `<tool_call>` markup is treated as attempted tool use, not narration: one **verbatim-tool-call** nudge asks the worker to re-issue a real `tool_call` and does not count toward the tool-less spiral. A missing envelope otherwise nudges once (**incomplete-report**) and a second tool-less turn still without the envelope salvages as **incomplete-report-stop** (once; later tool-less turns wait). Explore/read-only workers that used tools then replied with findings remain normal completes; `requireEvidence` (off by default, set per director) additionally requires at least one read before a tool-less spawn-only reply can complete. `requirePlanSubstance` (planner or `intent=plan`, not `modelRole === "plan"`) additionally requires Findings to contain files/paths, acceptance criteria, non-goals, risks, and ordered steps with a non-placeholder line each — four headings with stub Findings are incomplete-report, not an attachable plan. After real tool work, wrap-up Findings that are not placeholder or outline-only complete instead of being salvaged as a stub plan. Reads done through `run_shell` count as evidence too — `src/subagent/shell-evidence.ts` classifies shell reads (`cat`, `grep`, `sed` without `-i`, …) over the same subject expansion the auto-shell policy uses — but there is no corresponding shell-write evidence or file-write requirement: a run that never touches a file still completes normally once it replies with the envelope. There is no turn budget. Operator/parent cancel after any progress returns a **cancelled** salvage report (partial findings + tool activity) instead of a bare cancel string; cancel before progress still surfaces as cancelled-by-operator. There is no repetition/no-progress/never-acted/never-edited hard stop and no fingerprint-based re-dispatch block — a genuinely stuck worker runs until it completes, stalls, hits an opt-in wall-clock deadline, or is cancelled.
-  `spawn_agent` starts each worker and records it in the caller's fleet mailbox. On the TUI primary, mailbox mail is the collect path: occupancy takes uncollected terminals and re-enters the parent as system inbound with a Summary + Blockers digest (Findings when Summary is empty) and a blob pointer named for `read_file`. Nested orchestrators collect through mailbox mail the same way. A mounted `wait_agents` (exec primary) collects worker reports directly instead. Already-collected waits return status without a second report or error body. Wait JSON includes `stop_reason` from the session when present so a salvage that is wait-`done` is not mistaken for a clean complete, and so parent-initiated interrupt (`interrupted`) is not mistaken for operator-cancel (`cancelled`). Every terminal non-clean outcome (failed, cancelled, interrupted, or a forced-stop salvage) also carries a `failure` record, written in the same store mutation that makes the outcome visible and never rewritten: a typed `failure_class` (`provider_retryable`, `provider_fatal`, `loop_guard` for the reactor's doom-loop guard, the forced-stop reasons, or `error`), `recovery` availability with a typed reason, the attempt number, the ask_director `handoff` state at termination (`delivered` only when the worker's own ask_director call returned the answer), and whether `cleanup` released everything. `provider_failure` and `continuable` derive from that record, so wait_agents, list_agents, and mailbox mail cannot disagree. Deadline salvage prepends an advisory parent hint suggesting continuation plus a longer deadline if more wall-clock time is warranted. Failed and incomplete-report salvage tell the parent to diagnose from the report or error and MAY spawn one successor with a changed brief. A parent-initiated interrupt is a resumable pause: wait unblocks with `stop_reason: interrupted` (often while the session is still running and has no report); the parent should `resume_agent` or re-wait, and must not spawn a successor against a still-live worker. Successor only if that session is no longer resumable. Operator-cancelled salvage asks the parent to synthesize Findings and Paths and wait for the operator instead of auto-starting another specialist. Identical re-dispatch of the same brief stays refused at the prompt / spawn-handoff layer, except a recoverable/continuable child failure (`continuable: true`) MAY spawn one successor with the same brief; there is no fingerprint-based re-dispatch hard-block. Deadline hints are advisory only — an identical re-dispatch is still admitted at runtime. Parent hints are prepended on salvage reports returned to the parent. The runtime does not auto-spawn successors.
+  `spawn_agent` starts each worker and records it in the caller's fleet mailbox. On the TUI primary, mailbox mail is the collect path: occupancy takes uncollected terminals and re-enters the parent as system inbound with a Summary + Blockers digest (Findings when Summary is empty) and a blob pointer named for `read_file`. Nested orchestrators collect through mailbox mail the same way. A mounted `wait_agents` (exec primary) collects worker reports directly instead. Already-collected waits return status without a second report or error body. Wait JSON includes `stop_reason` from the session when present so a salvage that is wait-`done` is not mistaken for a clean complete, and so parent-initiated interrupt (`interrupted`) is not mistaken for operator-cancel (`cancelled`). Every terminal non-clean outcome (failed, cancelled, interrupted, or a forced-stop salvage) also carries a `failure` record, written in the same store mutation that makes the outcome visible and never rewritten: a typed `failure_class` (`provider_retryable`, `provider_fatal`, `loop_guard` for the reactor's doom-loop guard, the forced-stop reasons, or `error`), `recovery` availability with a typed reason, the attempt number, the ask_director `handoff` state at termination (`delivered` only when the worker's own ask_director call returned the answer), and whether `cleanup` released everything. `provider_failure` and `continuable` derive from that record, so wait_agents, list_agents, and mailbox mail cannot disagree. Deadline salvage prepends an advisory parent hint suggesting continuation plus a longer deadline if more wall-clock time is warranted. Failed and incomplete-report salvage tell the parent to diagnose from the report or error and MAY spawn one successor with a changed brief. A parent-initiated interrupt is a resumable pause: wait unblocks with `stop_reason: interrupted` (often while the session is still running and has no report); the parent should `resume_agent` or re-wait, and must not spawn a successor against a still-live worker. Successor only if that session is no longer resumable. Operator-cancelled salvage asks the parent to synthesize Findings and Paths and wait for the operator instead of auto-starting another specialist. Identical re-dispatch of the same brief stays refused at the prompt / spawn-handoff layer, except a recoverable/continuable child failure (`continuable: true`), which the parent recovers by calling `spawn_agent` with `recovers` set to the failed agent_id; there is no fingerprint-based re-dispatch hard-block. Recovery is enforced, not advisory: `recovery.available` requires a `provider_retryable` failure on the original spawn (not a resume_agent turn), no prior recovery, an original attempt (a failed replacement is `recovery_exhausted`), and a replay-safe run that touched only read, search, and web read tools (anything else is `side_effects_completed`). The claim lands synchronously before the handler awaits, so a duplicate or concurrent `recovers` call gets the existing replacement back and spawns nothing; an ineligible one is refused with its reason and never falls back to a plain spawn. The replacement is an ordinary spawn: it inherits no grants, approvals, or pending asks from the failed worker. Deadline hints are advisory only — an identical re-dispatch is still admitted at runtime. Parent hints are prepended on salvage reports returned to the parent. The runtime does not auto-spawn successors.
 
 #### Model-family policy (`src/agent/model-family-policy.ts`)
 

src/agent/prompts.ts

@@ -210,7 +210,7 @@ const GUIDELINE_SUB_BLOCKS: Record<
         (ctx.waitAgentsMounted
           ? " or re-wait"
           : ", or idle for its mailbox mail") +
-        "; do not `spawn_agent` a successor against a still-live worker. Successor only if that session is no longer resumable. Operator-cancel (`stop_reason` cancelled): wait for the operator; do not auto-retry. Identical brief: refuse. Recoverable/continuable child failure (`continuable: true`) MAY spawn one successor with the same brief; identical brief is still refused otherwise. Merge Summary/Findings into a coherent answer for the operator; do not paste raw fleet-agent dumps.",
+        "; do not `spawn_agent` a successor against a still-live worker. Successor only if that session is no longer resumable. Operator-cancel (`stop_reason` cancelled): wait for the operator; do not auto-retry. Identical brief: refuse. Recoverable/continuable child failure (`continuable: true`): recover it at most once with `spawn_agent` and `recovers` set to its agent_id; the runtime refuses any other recovery with a reason. Identical brief is still refused otherwise. Merge Summary/Findings into a coherent answer for the operator; do not paste raw fleet-agent dumps.",
       "- Use manage_tasks for your own coordination checklist; spawning workers is `spawn_agent`, not manage_tasks.",
       "- If context is compacted automatically, do not stop tasks early due to token fear; persist progress via manage_tasks and worker reports.",
     ];