feat(analytics): name setup failures and model-less chats so the activation ladder can read them

[Rinat S (rsolmano)]

Problem

The Growth & Retention dashboard shows ~65% of packaged installs never send a message, and on clean cohorts 48% boot the host and are never observed again. The consent-gated setup events meant to explain that were nearly useless: project_open failures all reported reason=unknown (the host threw plain Errors, so the existing not_git enum value was never populated), the native folder picker was unobserved, and a chat created with no usable model was indistinguishable from a configured custom provider — pi substitutes a {provider:"unknown"} placeholder model when none is given, so the if (created.model) guard in trackChatStarted never suppressed anything and such chats landed in the custom bucket.

Approach

Three closed-vocabulary additions, all host-mediated, none widening the privacy boundary (no paths, error text, or ids):

• Feature modules name their failures, the host maps the code. openProject throws CodedError("NOT_GIT") / CodedError("ALREADY_OPEN") — the same shared/codedError pattern pr and git already use — and failureReason() maps codes to the closed reasons. Nothing is ever derived from error text; every untyped failure stays unknown.
• The picker outcome is observed at the handler (dialog.selectDirectory), the only place the host sees it; a null path is cancelled.
• The none chat bucket is decided by the host's own new-chat resolution (defaults.model === null), not by sniffing pi's placeholder. For a resolved chat the created session's model is reported, because a session_start extension can call pi.setModel() during creation (regression-tested).

Reviewed in pair with gpt-6-astra; its must-fix on the extension case is what drove the defaults.model ? created.model : null wiring.

Changes

• packages/contracts: WsErrorCode gains NOT_GIT and ALREADY_OPEN (UI receives named codes on project.open rejections; errorText()-based flows are unchanged).
• packages/server/src/projects: openProject throws the two coded errors.
• packages/server/src/analytics: AnalyticsFailureReason gains already_open; SetupAction gains directory_pick; NONE_BUCKET exported.
• packages/server/src/host: failureReason() maps NOT_GIT/ALREADY_OPEN; dialog.selectDirectory wrapped in observeSetupAction("directory_pick", …, directoryPickOutcome); trackChatStarted emits provider/model = none, auth_method = unknown for model-less chats; both call sites pass defaults.model ? created.model : null.
• Tests: typed project.open rejection + picker succeeded/failed/cancelled with no path in the payload; model-less chat → none; startup extension switching the model → reported as the switched model.
• Specs: analytics, host, projects, contracts updated for the new vocabulary and the none rationale.

Dashboard side (no code, already live on PostHog 962459): install tiles filtered to build ≠ source, channel = stable; annotations for the v0.1.2–v0.1.3 app_installed gap; new HogQL tiles (first-boot activation ladder, os×build matched cohorts, readiness, setup outcome×reason, first-chat provider→send, first user-run outcome). Existing chat tiles should add provider != none once this ships.

Screenshots

Not applicable — no frontend changes.

Checklist

• Fast gates pass: bun run lint, bun run typecheck, bun run test — lint/typecheck/deps/boundaries/seams via the pre-commit hook on the final tree; bun run test → 1338 pass / 0 fail (18 packages); affected server tests re-run after rebase → 106 pass; bun run check:spec-surface → OK
• E2E suite passes for app-affecting changes (bun run e2e, or bun run e2e:full when touching agent behavior) — bun run e2e on the rebased tree → 465 passed, 8/8 shards. (A first post-rebase run had two e2e/layout.spec.ts failures — frontend group reorder / window placement, no web files in this diff — that passed on --last-failed and on the full re-run; noting it as a possible flake under 8-lane load after feat(web): replace the Resources popover with a trigger, dock and inspector #631.)
• Before/after screenshots are included for frontend changes, or marked not applicable
• Relevant SPEC.md / top-level specs updated to reflect any boundary, contract, or behavior change
• I have read the Contributing guide and agree to the Code of Conduct

[jetbrains-air]

Approved — ready to merge.