internal/model: Event, Report, Warning types and ordering

[Saber5656]

Title

internal/model: Event, Report, Warning types and ordering

Summary

Implement the canonical data types every other package exchanges: Event
(one activity record), the Report tree, Warning, the enums, and the
deterministic sort/dedup helpers, exactly as specified in DESIGN.md §6.2–§6.3
and §13.

Context

Providers (issues 09–15) emit []Event; aggregation (18) consumes them and
produces Report; renderers (20–21) and the LLM prompt builder (24) consume
Report. Deterministic ordering here is what makes golden-file testing
possible everywhere downstream.

Scope

• internal/model/event.go, report.go, warning.go, plus _test.go
  files. No I/O, no dependencies outside stdlib.

Detailed Requirements

1. Types exactly per DESIGN.md §6.2/§6.3:
   • type SourceID string with constants SourceZsh("zsh"),
     SourceGit("git"), SourceClaudeCode("claude-code"),
     SourceCodex("codex").
   • type EventKind string with KindCommand, KindCommit,
     KindAgentSession (values "command", "commit", "agent-session").
   • Event{Source, Kind, Start, End, Project, Ref, Title, Body, Meta}.
   • Warning{Source SourceID, Code, Message string} — Code values are the
     stable strings from DESIGN §13; define them as constants in this
     package (e.g. WarnZshNoTimestamps = "zsh_no_timestamps"), one constant
     per code listed there.
   • Report, ReportKind ("daily", "standup"), ProjectActivity,
     AgentSession, Commit, ShellActivity, CommandGroup, Totals,
     Narrative{Text, Model string}, GenerationMeta{Version string, Sources []SourceID, LLMModel string, RedactionMode string},
     StandupData{YesterdayDate string, Yesterday []ProjectActivity, Today []ProjectActivity, YesterdayShell, TodayShell ShellActivity, YesterdayTotals, TodayTotals Totals}.
   • Commit{Repo, Hash, Subject string, When time.Time, Files, Insertions, Deletions int}; AgentSession{Agent, Title, Ref string, Start, End time.Time, UserMsgs, AgentMsgs, Tasks int}; CommandGroup{Head string, Count int, First, Last time.Time, Examples []string};
     Totals{Commits, Insertions, Deletions, Sessions, AgentUserMsgs, Commands int, SpanStart, SpanEnd time.Time}.
2. Ordering helpers (pure functions, stable):
   • SortEvents([]Event) — by Start, then Source, then Ref, then Title.
   • SortProjects([]ProjectActivity) — activity score desc
     (3*len(Commits) + 2*len(Sessions)), then name asc — exactly the
     DESIGN §6.3 rule (shell commands are unattributed in v1 and never
     contribute to the score).
   • Within ProjectActivity: commits by When asc then Hash; sessions by
     Start asc then Ref; command groups by Count desc then Head asc.
3. Event.Validate() error — non-zero Start, known Source/Kind, End zero or
   ≥ Start.
4. Dedup helper DedupSessions([]Event) []Event — for KindAgentSession
   events with non-empty Ref, keep the first occurrence per (Source, Ref)
   pair; events with empty Ref are never deduplicated (unrelated sessions
   must not collapse); preserve order.
5. No JSON tags on Report yet except where needed by the LLM prompt
   builder later — add lower_snake_case JSON tags to all Report-tree structs
   now (they are also useful for tests).

Acceptance Criteria

• All types and constants above exist with the exact names/values.
• Sort helpers are deterministic under permutation (property-style table
  tests shuffle inputs and assert identical output).
• DedupSessions collapses two events with identical (Source, Ref) to
  one (the live-vs-archived Codex case) and never collapses events with
  empty Ref (two empty-Ref sessions stay two).
• Event.Validate rejects: zero Start, unknown Source, unknown Kind,
  End < Start — one test case each.
• Package has zero non-stdlib imports; ≥ 90% statement coverage.

Validation

go test -race -cover ./internal/model/ output pasted into the PR;
scripts/check_net_imports.sh still green.

Dependencies

01, 04 (Report.Range is a timeutil.Range; timeutil has no model
dependency, so no cycle).

Non-goals

Aggregation logic (18), warning emission (sources do that), rendering,
serialization formats beyond struct tags.

Design References

• docs/DESIGN.md §6.2, §6.3, §9.3 (ordering), §13 (warning codes)

---

Source of truth: docs/issues/03-model-package.md (PR #1, branch docs/v1-design). If this issue and the repo docs disagree, the docs win. Execution order and dependencies: docs/ISSUE_PLAN.md (this is issue 03 of 33).