feat: client-agnostic backend — workspace-relative source_uri (client + infra)

[riley0227]

Summary

Client + infra half of the client/backend separation. Removes the HOME bind mount entirely and switches the client to emit workspace-relative paths as the canonical source_uri so no absolute host paths ever cross the wire.

What changed

Client (ingestion pipeline)

• core-ingestion/src/types.ts, ix-cli/src/client/types.ts — PatchSource gains workspaceId?: string; source.uri is now documented as a workspace-relative POSIX path. HealthResponse gains schema_version?: number.
• ix-cli/src/cli/commands/ingest.ts:
  • Computes workspaceRoot + workspaceId (SHA-256 of workspaceRoot abs path) once per run.
  • Converts absolute paths to workspace-relative before dispatching to parseFile, buildGlobalResolutionIndex, and the parse pool, so every deterministic node/patch/edge/chunk ID hashes relative paths.
  • Tags every built patch's source with workspaceId.
  • loadExistingHashes now queries the backend with relative paths and maps the response back onto absolute keys.
  • On startup, compares /v1/health schema_version against CLIENT_EXPECTED_SCHEMA_VERSION = 2 and forces a clean re-ingest on mismatch (node IDs change when the graph format flips from absolute to relative).
• ix-cli/src/cli/config.ts — new absoluteFromSourceUri helper that joins a workspace-relative source_uri against the active workspace root for commands that still need to open files off disk.
• ix-cli/src/cli/format.ts — relativePath is a no-op for already-relative input.
• ix-cli/src/cli/commands/read.ts — resolves sourceUri via absoluteFromSourceUri before any fs.* call so the graph's relative paths still map to real files.

Infra

• docker-compose.standalone.yml — removed the HOME bind mount from the memory-layer service. Closes the privacy hole where the entire user HOME directory was bind-mounted (read-only) into the backend container.
• scripts/backend.sh, scripts/dev/shutdown.sh, scripts/install/install.sh — removed IX_HOST_MOUNT_ROOT / IX_CONTAINER_MOUNT_ROOT exports. dc() wrappers preserved for Windows/MINGW compose dispatch.

Must land with

ix-infrastructure/ix-memory-layer PR on feat/client-agnostic-backend → dev:

• Rewrites StalenessDetector to pure graph comparison (no java.nio.file).
• Bumps /v1/health schema_version to 2.
• Updates RoutesSpec / StalenessDetectorSpec accordingly.

Test plan

• Run ix map --force against a backend built from the paired backend branch. Confirm every patch's source.uri is workspace-relative and source.workspaceId is populated.
• Run ix read <symbol> and ix read <file> — confirm files still resolve via absoluteFromSourceUri.
• Confirm docker compose -f docker-compose.standalone.yml up starts cleanly with no HOME bind mount and memory-layer still serves /v1/health.
• Verify schema mismatch forces re-ingest: start backend on old image (schema_version 1 or absent) and confirm the CLI prints the mismatch warning and flips opts.force.
• Audit a handful of graph queries end-to-end (ix impact, ix overview, ix search).