fix(graph): persist + read node.Context so cat context works on a mounted .db (mache-b8fe72)

[jamestexas]

The bug (first-impression / headline feature)

mache … --infer projects 236 source files but 0 context files — the blog's headline differentiator cat context ("only the imports/types visible to this scope") is absent for every construct on a mounted or built .db.

Root cause (confirmed by tracing the data flow): node.Context is populated at ingest (engine_walk.go) and works in MemoryStore, but the SQLite path silently drops it:

• the nodes table had no context column,
• SQLiteWriter.AddNode never wrote it,
• neither read path (SQLiteWriter.GetNode, NodesTableReader.GetNode) selected it.

So vfs.ContextHandler always saw len(node.Context)==0 and served nothing. Same claim-vs-reality class as the earlier find_definition-broken-on-projection finding.

Fix (end to end)

• nodes gains a context BLOB column; AddNode persists n.Context (nil → NULL).
• Both GetNode paths select it. SQLiteWriter.GetNode must round-trip Context too, or the engine's two-pass write nulls it via INSERT OR REPLACE — exactly the Properties bug mache-d28eb1.
• NodesTableReader (the mount read path shared by SQLiteGraph + WritableGraph) selects context only when the column exists (new graph.ColumnExists), so old / leyline-produced nodes tables degrade to empty Context instead of erroring. Incremental builds ALTER the column in.

Tests (the gap was: no test covered the SQLite path)

• internal/ingest: writer persists to the context column (raw-SQL assert) + SQLiteWriter.GetNode round-trips it (two-pass protection).
• internal/graph: NodesTableReader.GetNode carries Context (mount path) + backward-compat when the column is missing.
• vfs.ContextHandler was already tested against node.Context; the chain is now covered ingest → persist → read → serve.

Verification

• go test ./internal/graph/ ./internal/ingest/ ./internal/vfs/ → ok
• -race on the round-trip/reader → ok
• go vet + golangci-lint (pre-commit) → pass

[github-actions]

find_smells (advisory)

Scoped to files changed in this PR. Rules below run on the standalone (no-LLO) cross-ref tables; _ast rules (cyclomatic_complexity, long_function, long_file, magic_int_in_comparison) are not exercised here.

untested_function — 1 finding(s) in changed files

Source	Node	Metric
internal/graph/nodes_table_reader.go	graph/functions/ColumnExists	0

god_file — 1 finding(s) in changed files

Source	Node	Metric
internal/ingest/sqlite_writer.go		117

Rules: the registry is cmd/smell_rules.go (source of truth); see the authoring guide to add one. Advisory only — these are heuristics, not gates.

[Copilot]

Pull request overview

This PR fixes a missing persistence/read-path for node.Context in the SQLite-backed graph so the context virtual file (used by cat context) works correctly when operating on a mounted or built .db.

Changes:

• Add a context BLOB column to the SQLite nodes table and persist node.Context during ingestion writes.
• Ensure both SQLite read paths (SQLiteWriter.GetNode and NodesTableReader.GetNode) round-trip Context, including guarding the mount reader for older DBs missing the column.
• Add targeted tests covering write persistence, read round-trip, and backward-compat behavior when the column is absent.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/ingest/sqlite_writer.go	Adds nodes.context schema + incremental ALTER, persists and reads Context in writer paths.
internal/ingest/sqlite_writer_test.go	Adds an ingest-side regression test ensuring Context is stored and round-trips via GetNode.
internal/graph/nodes_table_reader.go	Adds column detection and conditionally selects context for backward-compatible mount reads.
internal/graph/context_roundtrip_test.go	Adds graph-layer tests for mount-path context read and missing-column compatibility.

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