docs(backlog): capture everyday-atoms grounding pack idea (closed #449)

#449 shipped an inert, duplicated, unvalidated pack off-brief; closed it but kept
the on-thesis idea (ground the nouns GSM8K problems use) with the real scope it
would need to be beneficial.

docs/handoff/BACKLOG-everyday-atoms-grounding-pack.md

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+# Backlog: everyday-atoms grounding pack (idea, not yet scoped)
+
+**Source:** closed PR #449 (`atomic_definitions_everyday_v1`), opened off-brief by
+the remote connector during the 2026-05-29 ADR-0179 work. Closed as not-mergeable
+(inert, structurally duplicated, unvalidated, disconnected from the active arc),
+but the *idea* is worth keeping.
+
+## The idea
+
+A compact, curated pack of everyday-object atoms — the concrete nouns GSM8K word
+problems actually lean on (apples, baskets, boxes, strawberries, coins, …). This
+is on-thesis: it gives the engine "more pieces to the puzzle" so it can comprehend
+the entities a problem talks about, rather than only counting their numbers. It is
+*finding/comprehending better*, not *storing another found answer*.
+
+## Why #449 as shipped delivered no benefit
+
+- **Inert** — nothing in `chat/`, `generate/`, `language_packs/`, or `core/`
+  referenced it; `default = false`, `status = "draft"`. No runtime effect.
+- **Duplicated + mislocated** — shipped the same 9 files twice
+  (`packs/everyday/` *and* `packs/everyday/atomic_definitions_everyday_v1/`),
+  neither matching the flat `packs/<pack_id>/` convention (cf. `packs/en/`).
+- **Unvalidated** — never run through the pack gate (`core pack validate`); all
+  gates `false`; manifest checksums unverified (must hash the bytes on disk).
+- **Disconnected** — the math derivation/reader lane does not consume semantic
+  packs, so even if loaded it would do nothing for GSM8K today.
+
+## What would make it beneficial (the real scope when it's time)
+
+1. **One flat, conventional location**: `packs/atomic_definitions_everyday_v1/`.
+2. **Passes the pack gate**: probes green, checksums hashing the written bytes,
+   `validate_pack_dir`/`lift_from_pack` delegation reviewed at the dynamic-validator
+   trust boundary.
+3. **A consuming grounding path**: an ADR that wires everyday-atom grounding into a
+   comprehension/reader lane that actually reads it (otherwise it's a parked
+   artifact). Likely adjacent to the ADR-0178 comprehension-guided composer, not to
+   ADR-0179 extraction.
+4. **Curated, not bulk** — keep it compact (CLAUDE.md: no corpus bulk-ingest into
+   runtime); grow it deterministically with pack tests.
+
+Until 1–3 exist, this is an idea, not a pack.