fix(packages): continue past failed installs; write MigrationReport on restore

[dipto0321]

Summary

The previous installPackages() returned on the first failed npm install -g, so a single broken / renamed / yanked package silently aborted the migration of every package after it. A user upgrading 30 globals where #3 fails lost 27 packages with no visible signal. Plus the entire MigrationReport.Save() / report.go path was dead code — the file shipped but was never called. Three concerns, same root cause: package install failures were treated as fatal instead of informational. Now treated as data.

Changes

• internal/packages/snapshot.go — installPackages now LOOP-ALL. ctx.Err() is checked at the top of each iteration so Ctrl-C still aborts promptly; only per-package npm failures continue. Returns ([]PackageResult, error) where the slice is populated for every package attempted (success or fail) so callers can build a MigrationReport. Aggregate error wraps the first failure with an "N of M packages failed" headline and preserves the original via %w. Restore and RestoreFromSnapshot return a RestoreOutcome struct (parsed snapshot + per-package results) so callers can populate MigrationReport metadata without re-parsing the snapshot.

• internal/packages/snapshot.go — package-level runShell test seam so the install loop is unit-testable without spawning a real npm. Tests must NOT call t.Parallel() — the seam is package-global, same pattern fnm.go uses.

• internal/packages/report.go — Path() returns a stable filename per-report (with a 4-byte crypto/rand tag to prevent sub-second collisions), and Save() uses the same path. Save is NOT safe to call concurrently on the same instance, but no real caller does.

• internal/cli/upgrade.go — builds a MigrationReport on every restore (success or partial) using the snapshot's recorded manager / from-version when available. Skips the write on empty results. Partial failure keeps sentinel armed (restoreSucceeded stays false), so nodeup packages restore --from <path> still works for retry.

• internal/cli/packages.go — same report write on both --from and positional branches; report reflects the snapshot's recorded manager / from-version so the --from branch gets accurate metadata instead of "unknown".

• internal/packages/snapshot_test.go — 6 new tests covering loop-all behavior (table-driven 5 packages with 2 mid-list failures), all-success, ctx-cancel mid-loop, empty list, MigrationReport path stability + content round-trip, and report path collision resistance between two reports created in the same wall-clock second.

• internal/packages/sentinel_test.go — updated for the new RestoreFromSnapshot signature.

Sentinel semantics on partial failure

restoreSucceeded only flips to true when zero packages failed. On partial failure, the sentinel stays armed and the user can re-run nodeup packages restore --from <snapshot-path> to retry the failed packages — the report file (always written, success or partial) tells them which ones failed. Documented inline at upgrade.go:88-103.

Verification

• go test -race ./internal/packages/... — green
• make ci — green (golangci-lint: 0 issues; coverage: 62.8%)
• 6 new tests pin the loop-all + report-write behavior
• 1 new test pins sub-second report path collision resistance (4-byte crypto/rand suffix)

Closes #103.

[cocogitto-bot]

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