Register AGENTIC-WP-0006 (error-body mining) workplan

Captures normalized error fingerprints into the durable digest and clusters
recurring root-cause errors across sessions — closes the content-level 'why' gap
called out in the friction assessment. 3 tasks; we implement this in helix_forge.
(State Hub skill handed off to the state-hub worker as STATE-WP-0058.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

workplans/AGENTIC-WP-0006-error-body-mining.md

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+---
+id: AGENTIC-WP-0006
+type: workplan
+title: "Coding Session Memory — Error-Body Mining (content-level root causes)"
+domain: helix_forge
+repo: agentic-resources
+status: ready
+owner: codex
+topic_slug: helix-forge
+created: "2026-06-07"
+updated: "2026-06-07"
+state_hub_workstream_id: "c6e44147-15fd-4cfa-ab2d-87461a6858f1"
+---
+
+# Coding Session Memory — Error-Body Mining
+
+The friction assessment ([ASSESSMENT-infra-friction.md](../docs/ASSESSMENT-infra-friction.md))
+can see *that* a session was expensive (tool-mix, cost, overhead share) but not
+always *why* at the content level — the specific error messages and repeated
+failed approaches. The digest captures tool histograms and prompt/response
+snippets, but **not error-body text**. This workplan closes that gap so Detect can
+surface recurring root-cause errors, not just coarse markers.
+
+Approach: capture **normalized error fingerprints + samples into the durable Tier 2
+digest** (raw Tier 1 blobs are evictable, so mining must persist into the digest),
+then cluster recurring fingerprints across sessions into candidate problem
+patterns through the existing clusterer. No new capture source — this reads the
+event/blob bodies already ingested.
+
+## Capture Error-Body Snippets into the Digest
+
+```task
+id: AGENTIC-WP-0006-T01
+status: todo
+priority: high
+state_hub_task_id: "136a0a73-61c2-4390-876c-de3880a967e6"
+```
+
+Extend `core/digest.py` `build_digest` to extract, from failed events
+(`kind=error` and `tool_result` bodies matching the existing `_FAIL_HINTS`), a
+**normalized fingerprint** (strip paths, line numbers, UUIDs, hex) plus a short
+sample, stored as `digest["error_snippets"] = [{fingerprint, sample, count, tool}]`.
+Same error across a session collapses to one fingerprint with a count. Durable in
+Tier 2 (survives Tier 1 eviction). Bump `SCHEMA_VERSION`. Unit-tested on synthetic
+sessions with repeated and varied errors.
+
+## Recurring-Error Signal + Clustering
+
+```task
+id: AGENTIC-WP-0006-T02
+status: todo
+priority: high
+state_hub_task_id: "1a41b6f5-48bc-4080-bd18-94f2186ef566"
+```
+
+Add `detect/signals.py` `sig_recurring_error` keyed on the error fingerprint, so
+the same error recurring across sessions/repos/flavors clusters into a candidate
+problem pattern (locus = fingerprint; magnitude = occurrences). Feeds the existing
+clusterer + cross-flavor flagging, so a root-cause error common to multiple flavors
+is flagged cross-flavor. Respects the WP-0005 quality filter. Unit-tested on
+synthetic digests sharing a fingerprint.
+
+## Re-run Live, Extend Friction Assessment with Root Causes
+
+```task
+id: AGENTIC-WP-0006-T03
+status: todo
+priority: medium
+state_hub_task_id: "bed16d23-3971-4257-b066-d1e639fef150"
+```
+
+Re-ingest (to populate `error_snippets` — schema bump invalidates old digests) and
+re-run detect over the real local sessions. Add a **"content-level root causes"**
+section to [ASSESSMENT-infra-friction.md](../docs/ASSESSMENT-infra-friction.md):
+top recurring error fingerprints with counts and affected repos/flavors. Full suite
+green. After workplan updates, notify the operator to run from `~/state-hub`:
+
+```bash
+make fix-consistency REPO=agentic-resources
+```