feat(kernel): port grounding-layer from daemon (aegis#446 epic shipped 2026-04-14)

[stackbilt-admin]

Summary

Daemon shipped the grounding epic (aegis#446/#447/#450/#500) 2026-04-14, landing in daemon v1.98.1→v1.99.5. The core work is captured in `web/src/kernel/grounding-layer.ts` (277 LOC) plus companion changes to the executor registry. Zero of this is upstream in core.

Why it belongs in core

The Chimera class of bugs the grounding epic resolved — models inventing schemas, guessing API shapes, fabricating file paths — is not specific to the daemon. Any aegis variant consuming the core router + dispatch loop will hit the same failure modes. Grounding is an architectural property of the dispatch substrate, not a Stackbilt feature.

Referenced by `executor-registry.ts:127-139` (gap-signal count gate for tier escalation, aegis#497) — so the gap-signal writer lives in `kernel/procedural.ts` and the reader lives in `kernel/executor-registry.ts`. Both substrates are already in core; the grounding layer that writes the signals is the missing middle.

Acceptance criteria

• `web/src/kernel/grounding-layer.ts` ported to core with full public API
• Companion changes to `kernel/executor-registry.ts` reviewed for core vs daemon split (gap-signal reading is generic; Stackbilt-specific thresholds stay daemon-side if any)
• Subpath export added: `"./kernel/grounding-layer"`
• Core schema additions for grounding-gap tracking migrated (pairs with core: route procedural reads through a derived-stats compat helper (supports daemon aegis#564 Phase 2) #30 Phase 3 — the `grounding_gap` column on `episodic_memory`)
• Router integration point: core's `kernel/router.ts` calls into the layer at the dispatch boundary
• Unit tests ported

Dependencies

• Should sequence after aegis-oss#30 lands (procedural compat helper) — the grounding-gap substrate migration lives most naturally in core: route procedural reads through a derived-stats compat helper (supports daemon aegis#564 Phase 2) #30's Phase 3 (migrating gap signals off `procedural_memory.gap_signal_count` onto `episodic_memory.grounding_gap`).

Out of scope

• Tool-call log cross-check + auto-strip + classifier split — deferred in daemon memory per `project_grounding_epic.md` pending production signal
• Daemon-specific grounding rules that reference Stackbilt substrates — stay daemon-side

References

• Daemon: `web/src/kernel/grounding-layer.ts` (277 LOC)
• Epic trail: aegis#446, #447, #450, #500 (all closed)
• Memory: `project_grounding_epic.md`
• Related: aegis#497 (tier escalation gate — consumes gap signals)