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diff --git a/openspec/changes/log-invite-outcomes/specs/invite-observability/spec.md b/openspec/changes/archive/2026-11-01-log-invite-outcomes/specs/invite-observability/spec.md
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+# invite-observability Specification
+
+## Purpose
+Emit one structured log event per invite-processing branch (request handling and Slack response) so any failure — including Slack error strings the worker does not yet know — is identifiable in Workers Logs, later Grafana dashboards, and incident reports, while user-facing page responses stay unchanged.
+
+## Requirements
+
+### Requirement: Log one invite_outcome event per processed invite submission
+
+Every `POST /invite` request that reaches a terminal branch MUST log exactly one structured event with `event: 'invite_outcome'`, `outcome` (`'success'` or `'failure'`), `detail` (a stable short branch key), and `slack_error` whenever Slack returned `ok: false`.
+
+#### Scenario: Success
+
+- **WHEN** Slack returns `ok: true`
+- **THEN** the log carries `outcome: 'success'`, `detail: 'invited'`, and no `slack_error` field.
+
+#### Scenario: Mapped Slack errors keep their string
+
+- **WHEN** Slack returns `already_invited`, `already_in_team`, or `invalid_email`
+- **THEN** the log carries that exact string in `slack_error`, with `outcome: 'success'` for the first two and `outcome: 'failure'` for `invalid_email`.
+
+#### Scenario: Unmapped Slack error is still visible
+
+- **WHEN** Slack returns an error string the worker does not map
+- **THEN** the response is the regular failure page (HTTP 200), and the log carries `outcome: 'failure'` with `slack_error` equal to the verbatim string.
+
+#### Scenario: Slack call fails before a response
+
+- **WHEN** the Slack HTTP call rejects
+- **THEN** the log carries `outcome: 'failure'`, `detail: 'slack_unreachable'`.
+
+#### Scenario: Unexpected exception
+
+- **WHEN** an uncaught error terminates the request
+- **THEN** the log carries `outcome: 'failure'`, `detail: 'unexpected_error'`.
+
+### Requirement: Log non-Slack invite branch failures
+
+Failures that terminate the request before the Slack call MUST be visible as `invite_outcome` events with `outcome: 'failure'` and a stable `detail` key, additive to any existing log events. Requests that never reach an invite branch MUST NOT log the event.
+
+#### Scenario: Missing email
+
+- **WHEN** a submission has no email value
+- **THEN** the log carries `detail: 'missing_email'` with `outcome: 'failure'`.
+
+#### Scenario: Rejected Turnstile
+
+- **WHEN** the Turnstile siteverify call returns `success: false` for a form submission
+- **THEN** the response is the verification-failed page (HTTP 403), and the log carries `detail: 'verification_failed'` with `outcome: 'failure'`.
+
+#### Scenario: Missing secrets
+
+- **WHEN** a required secret is unset
+- **THEN** the log carries `detail: 'secrets_missing'` with `outcome: 'failure'`, alongside the existing `secrets_missing` event.
+
+#### Scenario: Turnstile call error
+
+- **WHEN** the Turnstile verification call fails to complete
+- **THEN** the log carries `detail: 'verification_error'` with `outcome: 'failure'`, alongside the existing `turnstile_verify_error` event.
+
+#### Scenario: Bot probes stay quiet
+
+- **WHEN** a request serves static assets or a plain 404
+- **THEN** no `invite_outcome` event is logged.
+
+### Requirement: Log invite_outcome without personal data
+
+`invite_outcome` events MUST NOT contain email addresses or other user-supplied personal data.
+
+#### Scenario: Success event carries no PII
+
+- **WHEN** an invite succeeds for any email address
+- **THEN** the logged event holds only branch identity and Slack metadata, with no field carrying the submitted email value.