atlas-scatter

name	atlas-scatter
description	Phase L sub-mode (Scatter-Gather Locate) — TRANCE-gated parallel fan-out of read-only Locate probes across topologically-disjoint module clusters, each in a clean-context subagent, merged back into findings.md via a deterministic dedup contract. Never default; serial Locate is the standard path. Use ONLY when map.md surface is large (>5 modules OR >25 files) AND ≥2 disjoint DECISION_TARGET sub-questions exist. Trigger phrases — "audit across all modules", "trace these N independent flows", "scout this large surface in parallel". Do NOT load for a single sub-question, tightly-coupled sub-questions, or a tight budget.
allowed-tools	search_symbol graph_query search_text view_file test_dry_run memex_read
metadata	{"methodology":"ATLAS","phase":"L"}

SKILL: Scatter-Gather Locate (Phase L sub-mode)

When to use

Load when: map.md is complete AND the activation trigger below fires. This is the operationalized G1 TRANCE form of the diffuse scatter primitives already in skills/locate.md (Operator pattern) and agent.md P0 rule 7.

Unload when: every sub-question has ≥1 merged finding at confidence ≥ M or a GAP, and the merged findings.md has entered the Phase A fold.

This mode does not add capability — it adds parallelism. It is still read-only (I-1). Scatter never grants a write tool, never resets the budget, and never escapes a refusal gate. Branch budgets sum to ≤ the parent budget.

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Activation trigger (both-flags rule — TRANCE-gated)

Scatter-Gather is GATED, never default. Standard-tier Locate stays serial. Both flags MUST hold (cortex C5 + C6). If either is false, the mode is inert and you run the serial probe ladder in skills/locate.md.

Flag	Source	Threshold
Surface size (C5)	map.md MAP-MODULES / file count	> 5 modules OR > 25 files in scope
Disjoint sub-questions (C6)	mission.md DECISION_TARGET decomposition	≥ 2 topologically-disjoint sub-questions (different modules / concerns)

Either flag alone → stay standard tier (serial Locate). Both flags → escalate to the Scatter-Gather sub-mode.

When NOT to scatter (carry-through from locate.md)

• Only one sub-question exists.
• Sub-questions are tightly coupled (one's answer feeds another's probe).
• Budget is already tight — coordination overhead outweighs the parallel win.

In any of these, do not scatter. Run serial Locate.

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Fan-out plan (bounded, deterministic partition)

1. Derive the partition deterministically. Run a single parent-side graph_query("callgraph_slice: <scope>") (or, if unavailable, partition by MAP-MODULES centrality clusters from map.md). Do not LLM-guess the clustering — the partition is a structural fact, not an inference (see skills/locate.md Tier-2 graph-first decomposition).
2. One sub-mission per disjoint cluster, mapped 1:1 to a disjoint sub-question where possible.
3. Hard cap: 5 branches (cortex C1; orchestrator-worker sweet spot ~5). If the partition yields > 5 clusters, merge the lowest-centrality clusters until N ≤ 5.
4. Per-branch budget = parent_remaining / N. Budgets are partitioned, not multiplied. The sum of branch budgets MUST NOT exceed the parent's remaining budget.

Diversity is scope-diversity, not redundancy. Branches probe different modules. Do not spawn N identical probes of the same module — quality of the partition dominates redundant diversity.

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Sub-mission spec (Operator pattern, clean context)

Each branch is an ephemeral clean-context subagent seeded with ONLY its scope-slice + one sub-question + its budget. The clean context is the point: it prevents trajectory self-conditioning (no branch sees another branch's path). Reuses the locate.md sub_mission YAML, tightened:

sub_mission:
  parent_mission_id: <MISSION-ID>
  branch_id: <1..N>
  question: <one disjoint sub-question>
  scope: <path globs for this cluster only>
  budget:
    max_tool_calls: <parent_remaining / N>
    max_tokens_input: <parent_remaining / N>
  map_excerpt: <ONLY the MAP-MODULES + MAP-GRAPH slice for this cluster>

Each branch runs the Tier 1–5 probe ladder (skills/locate.md) within its scope and returns exactly one structured object — no transcript (I-4):

return:
  branch_id: <1..N>
  findings: [FINDING-XXX, ...]   # branch-local IDs
  gaps: [GAP-XXX, ...]
  ruled_out: [<negative result notes>, ...]
  telemetry: {tokens_used, tool_calls}
  # NO transcript. NO raw tool outputs. Excerpts go to Memex.

The parent never ingests branch transcripts. Branch working state is destroyed on return.

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Merge + dedup contract (two-stage bounded gather)

Stage 1 — Gather & dedup (parent-side, deterministic)

1. Renumber to global IDs. Branch-local FINDING-XXX / GAP-XXX ids are renumbered to a global namespace to avoid cross-branch collision.
2. Dedup on mechanical fields first. Merge two findings into one when they match on (path, overlapping line-range); use claim-equivalence only as a tiebreak. The merged finding keeps the highest confidence tier and unions the evidence anchors and ruled_out notes.
3. Contradictions are NOT silently merged. When two branches make conflicting claims about the same anchor, emit a single finding marked [DISPUTED] (D7) carrying both claims, and drop it to confidence L pending a follow-up probe. Do not pick a winner mechanically.

Stage 2 — Fold (reuse existing machinery)

The merged findings.md flows unchanged into the existing Phase A clean-context fold (skills/abstract.md). No new aggregator is built — the AgentFold subagent already aggregates; scatter merely feeds it a merged list instead of a serial one.

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Stop condition (explicit — D5)

Scatter completes when every sub-question has ≥1 merged finding at confidence ≥ M OR a GAP. Scatter does not re-spawn: max recursion remains 1 (agent.md P0 rule 9). A branch that returns only L/empty triple records a GAP; the parent does not re-scatter that cluster.

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Telemetry

Record at the gather edge:

scatter | branches: N | fan_out_ratio: <sum(branch_tokens)/serial_estimate>
        | dedup_count: <merged-away> | disputed: <count> | tool_calls: <sum>

fan_out_ratio and dedup_count are the feedback signals: a low dedup count on overlapping scopes means the partition was too coarse; a high one means the clusters were not actually disjoint (revisit the trigger).

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Exit gate

• Both activation flags verified against map.md + mission.md before scattering (else serial Locate).
• Partition derived from a deterministic graph/centrality query, ≤ 5 branches.
• Each branch ran clean-context, returned one object, no transcript (I-4).
• Per-branch budgets sum to ≤ parent remaining budget.
• Merged findings.md: global ids, dedup on path/line, [DISPUTED] on contradiction (never silent-merge).
• Every sub-question has a finding ≥ M or a GAP; no re-scatter.
• Merged findings entered the Phase A fold; telemetry recorded.