inception(skills): inception-entry skill scaffold + bridge plumbing

[leeovery]

Summary

Phase 2 of the inception/discovery-map initiative — establishes the inception door.

• New workflow-inception-entry/ skill (SKILL.md + validate-phase.md, gather-context.md, invoke-skill.md). First-session path is fully wired; refinement re-entry is a structural placeholder that emits a "coming in a later phase" stub. Modeled on workflow-research-entry.
• New workflow-bridge/references/inception-continuation.md — plan-mode handoff that always re-invokes /continue-epic {work_unit}. Bridge SKILL.md Step 2 gains a completed_phase = inception guard placed above all work-type branches so non-inception epic completions still fall through to epic-continuation.md.
• continue-epic/scripts/discovery.cjs — 'inception' added as the first entry in EPIC_PHASES so the iterators recognise the new phase. No display change; render lands in Phase 5.

By design — Phase 2 is intentionally unreachable end-to-end

• No user-visible behaviour change. /start-epic still routes to research/discussion as it does today (wiring lands in Phase 4).
• The entry skill exists but invoking it errors at Step 5 because workflow-inception-process ships in Phase 3.
• invoke-skill.md and inception-continuation.md reference skills that don't exist yet on this branch — markdown links are valid; runtime errors are expected. Phase 3 lights it up.
• Refinement (re-entry) is stubbed, not skipped — validate-phase.md has the structural placeholder; Phase 6 replaces the body with the real flow.

Implementation notes

• No Step 0 in workflow-inception-entry — non-user-invocable entry skills omit it; the parent (start-epic / continue-epic) runs migrations + knowledge-check. Same precedent as workflow-research-entry and workflow-discussion-entry.
• Workflow-context table is 7-phase, epic-only — only inception's table renumbers. Other entry skills' tables stay 6-phase until Phase 13.
• Phase entry detection uses exists '{wu}.inception.*' (wildcard topic) — false → first-session, true → refinement.

Test plan

• All 214 workflow-manifest tests pass (bash tests/scripts/test-workflow-manifest.sh)
• discovery.cjs runs cleanly on a synthetic epic with no phases.inception (legacy shape regression check)
• discovery.cjs iterates inception items cleanly when present (no shape errors in buildEpicDetail)
• exists '{wu}.inception.*' returns false on a fresh epic, true after init-phase {wu}.inception.{topic}
• Mental compliance walk-through against compliance-check.md on every new and modified skill file

Branch / merge ordering

Stacked on idea/inception-rephase (PR #266). Will be rebased onto main after Phases 1 and the rephase doc-PR land in turn — see discovery-map/INDEX.md for the full table.

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