plans: add phase 6 zero projection

plans/git-native-kb/06-zero-projection.md

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+# Phase 6 — Zero / real-time projection
+
+> Depends on Phases 3/4. The one genuinely net-new subsystem (partly offsets the deletions). Umbrella: [`00-umbrella-plan.md`](00-umbrella-plan.md).
+
+## Objective
+
+Keep the real-time web UI working after git becomes the source of truth. The UI is driven by Zero (Postgres logical replication, `zero_publication.py`); git is not a real-time source, so we project git state → the Zero-published `documents`/`folders` rows after each commit.
+
+## Locked model
+
+- **One-way projection (git → Postgres rows), not a second source of truth.** The projected `documents`/`folders` rows are **thin metadata for the UI** (title, path, folder tree, timestamps) — content authority stays in git; chunks/embeddings stay derived (Phase 4). This preserves the "no two-way sync" rule.
+- **Driven by the commit event** (Phase 3). Simplest owner: extend the Phase-4 post-commit indexer to also upsert/delete the Zero-published rows in the same pass.
+- Zero publication column lists (`zero_publication.py`) stay as-is; we just keep the rows current from git.
+
+## Work items
+
+1. `project_commit(workspace_id, sha)` — from the tree diff, upsert `documents`/`folders` metadata rows and delete rows for removed paths; publish via the existing Zero path.
+2. Decide owner: fold into Phase-4 `index_commit` (one post-commit pass) vs. a separate projector task — default: fold in.
+3. Ensure ordering: commit → index + project atomically enough that the UI never shows a file with no metadata row (or vice versa).
+
+## Tests
+
+- After a commit, Zero-published `documents`/`folders` rows reflect the new tree within the projection cycle.
+- Deleting a file removes its row; renaming updates path/title.
+- A workspace with the flag on stays live in the web UI end-to-end (create/edit/delete visible).
+
+## Out of scope
+
+- Replacing Zero with a git-aware sync (not now).
+- Frontend changes beyond keeping current behavior (separate umbrella).
+
+## Open questions
+
+1. Projection owner: indexer hook vs. dedicated projector (default: indexer hook).
+2. Consistency model: are index + projection in one transaction/pass, or eventually consistent with a short lag?
+3. Do any Zero-published columns need content that isn't cheap to derive from the tree (forces a richer projection)?