feat: use embedded postgres on Windows

[mattjohnsonpint]

Modus requires a database for persistence of:

• Plugin metadata
• Inference history
• Agent state

Before this PR, PostgresDB was used in production, and ModusGraph was used in development for Linux and macOS. However, since ModusGraph does not currently support Windows, there was no story for persistence on Windows at all, other than to manually spin up and configure a separate local Postgres server or Docker container.

Since Agent state requires persistence, it's important that we have a better story for Windows developers.

With this PR, a pseudo-embedded Postgres instance can be automatically created and used when needed. It is enabled by default for local development on Windows. It can also be manually enabled on other OSs (eg., for testing), by setting an environment variable MODUS_DB_USE_EMBEDDED_POSTGRES=true.

When enabled, a local postgres instance will automatically start and stop with the Modus Runtime. The data files for the local database will be in a .postgres folder in the project directory. The same queries used for Postgres in production will be used for the local database, and the DB migrations are applied automatically.

[linear]

HYP-3374 Modus persistence on Windows

[trunk-io]

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[Copilot]

Pull Request Overview

Adds embedded Postgres support on Windows (and optionally other OSes) to replace the manual Postgres setup for local development.

• Introduces a new embeddedpg.go implementation that auto-starts/stops Postgres and runs migrations.
• Updates db.Initialize/db.Stop to hook into embedded Postgres when enabled; refactors useModusDB logic.
• Cleans up .gitignore, VSCode launch configs, and adds necessary Go module dependencies.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk/go/examples/agents/.gitignore	Ignore new .postgres/ folder
sdk/assemblyscript/examples/agents/.gitignore	Ignore new .postgres/ folder
runtime/services/services.go	Log “Shutdown complete.” after services stop
runtime/go.mod	Add embedded-postgres, migrate, lib/pq, xi2/xz; add replace
runtime/explorer/explorer.go	Remove Windows stub and enable inference history endpoint
runtime/db/modusdb.go	Simplify InitModusDb guard; refactor addToGitIgnore
runtime/db/embeddedpg.go	New embedded Postgres support with migrations and shutdown
runtime/db/db.go	Wire embedded Postgres into Initialize and Stop
.vscode/launch.json	Remove hard-coded MODUS_DB env from launch configs
.trunk/configs/cspell.json	Add new terms (embeddedpostgres, fergusstrange, iofs)

Comments suppressed due to low confidence (3)

runtime/db/embeddedpg.go:98

• [nitpick] The variable name d is ambiguous; rename it to something like migrationSource to clarify its role.

d, err := iofs.New(migrationsFS, "migrations")

runtime/db/embeddedpg.go:103

• [nitpick] The variable m is non-descriptive; consider renaming it to migrator or migrationEngine for clarity.

m, err := migrate.NewWithSourceInstance("iofs", d, cs)

runtime/db/embeddedpg.go:36

• There are no accompanying unit or integration tests for the new embedded Postgres flow; adding tests for useEmbeddedPostgres, findAvailablePort, and prepareEmbeddedPostgresDB would improve confidence in this feature.

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