Why: The completion proposal defines the N1/Q1/I1 phases but not their
work packages; D1 has landed, so the three phases are now unblocked and
need file-level plans grounded in the current pins.
Evidence: docs-only change; file:line claims verified against the pinned
worktrees (native 3a110a7, squad 5a57636, intent 65aaebc, backend
e7fb276).
Impact: Adds one proposal and one link line; no code changes.
Refs: docs/proposals/2026-10-02-agent-stack-completion.md
weichen
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