diff --git a/src/draft/command_create.py b/src/draft/command_create.py
index 54d431c..3ce7c43 100644
--- a/src/draft/command_create.py
+++ b/src/draft/command_create.py
@@ -599,6 +599,15 @@ def run(args) -> int:
         worktree_mode,
     )
 
+    try:
+        from draft.steps.implement_spec import original_spec
+
+        label = original_spec.preamble_label(ctx)
+        if label:
+            print(f"original-spec: attached from {label}", file=sys.stderr)
+    except Exception:
+        pass
+
     # 14. Lifecycle + engine
     engine = Runner()
     lifecycle = DraftLifecycle(
diff --git a/src/draft/runs.py b/src/draft/runs.py
index f6c0ad2..76f0469 100644
--- a/src/draft/runs.py
+++ b/src/draft/runs.py
@@ -45,6 +45,12 @@ def _run_started_at(run_dir: Path) -> float | None:
         return None
     try:
         return parse_human(started).timestamp()
+    except (ValueError, TypeError):
+        pass
+    try:
+        from datetime import datetime
+
+        return datetime.fromisoformat(started.replace("Z", "+00:00")).timestamp()
     except (ValueError, TypeError):
         return None
 
@@ -119,6 +125,24 @@ def is_run_finished(state: dict) -> bool:
     return all(s in state.get("completed", []) for s in expected_steps(state))
 
 
+def find_original_run_on_branch(project: str, branch: str) -> Path | None:
+    candidates = []
+    for run_dir in project_runs(project):
+        state = load_state(run_dir)
+        if state is None:
+            continue
+        data = state.get("data", {})
+        if data.get("branch") != branch:
+            continue
+        if data.get("branch_source") != "new":
+            continue
+        started = _run_started_at(run_dir) or 0.0
+        candidates.append((started, run_dir))
+    if not candidates:
+        return None
+    return min(candidates, key=lambda x: x[0])[1]
+
+
 def find_active_run_on_branch(project: str, branch: str) -> Path | None:
     from draft.pipelines import CorruptStateError
 
diff --git a/src/draft/steps/implement_spec/__init__.py b/src/draft/steps/implement_spec/__init__.py
index fdc0954..d937961 100644
--- a/src/draft/steps/implement_spec/__init__.py
+++ b/src/draft/steps/implement_spec/__init__.py
@@ -8,6 +8,7 @@
 from pathlib import Path
 
 from draft.hooks import HookResult, _run_hook_cmd
+from draft.steps.implement_spec import original_spec
 from draft.steps.implement_spec._live_status import LiveStatusSummarizer
 from pipeline import Step, StepError
 from pipeline.runner import TIMEOUT_EXIT
@@ -30,7 +31,7 @@ def _render_verify_commands(entries: list[dict]) -> str:
         return ""
     block = "\n".join(cmds)
     return (
-        "## Verify commands\n\n"
+        "## Verified commands\n\n"
         "Draft will run the following after your changes. "
         "Run them yourself before finishing if practical.\n\n"
         f"```bash\n{block}\n```"
@@ -39,18 +40,35 @@ def _render_verify_commands(entries: list[dict]) -> str:
 
 def _render_prompt(ctx, template: str, verify_commands: str) -> str:
     spec = ctx.get("spec", "")
+    spec_section = f"## Current Spec\n\n{spec}"
     verify_errors = ctx.step_get("implement-spec", "verify_errors", "")
     if verify_errors:
-        verify_section = f"## Test failures\n\n{verify_errors}\n\nFix the above failures before committing."
+        verify_section = f"## Verified errors\n\n{verify_errors}\n\nFix the above failures before committing."
     else:
         verify_section = ""
+    original_spec_section = original_spec.render_original_spec(ctx)
     return (
-        template.replace("{{SPEC}}", spec)
-        .replace("{{VERIFY_COMMANDS}}", verify_commands)
+        template.replace("{{VERIFY_COMMANDS}}", verify_commands)
+        .replace("{{ORIGINAL_SPEC}}", original_spec_section)
+        .replace("{{SPEC}}", spec_section)
         .replace("{{VERIFY_ERRORS}}", verify_section)
     )
 
 
+def _log_prompt(log_path, prompt: str, attempt: int, max_attempts: int) -> None:
+    ts = datetime.now(UTC).strftime("%Y-%m-%dT%H:%M:%SZ")
+    block = (
+        f"=== implement-spec prompt (attempt {attempt}/{max_attempts}) @ {ts} ===\n"
+        f"{prompt}\n"
+        f"=== end prompt ===\n\n"
+    )
+    try:
+        with open(log_path, "a", encoding="utf-8") as f:
+            f.write(block)
+    except OSError as exc:
+        print(f"warning: could not write prompt log {log_path}: {exc}", file=sys.stderr)
+
+
 def _has_changes(cwd: str) -> bool:
     result = subprocess.run(
         ["git", "status", "--porcelain"],
@@ -355,8 +373,15 @@ def run(self, ctx, engine, lifecycle, step_metrics):
                         prefix=prefix,
                     ).start()
                 try:
+                    prompt = _render_prompt(ctx, impl_template, verify_commands)
+                    _log_prompt(
+                        ctx.log_path(self.name),
+                        prompt,
+                        attempt=attempt,
+                        max_attempts=cfg["max_retries"],
+                    )
                     engine.run_llm(
-                        prompt=_render_prompt(ctx, impl_template, verify_commands),
+                        prompt=prompt,
                         cwd=wt_dir,
                         log_path=ctx.log_path(self.name),
                         step_metrics=step_metrics,
diff --git a/src/draft/steps/implement_spec/implement_spec.md b/src/draft/steps/implement_spec/implement_spec.md
index 85c4676..280e697 100644
--- a/src/draft/steps/implement_spec/implement_spec.md
+++ b/src/draft/steps/implement_spec/implement_spec.md
@@ -13,7 +13,7 @@ You must not run `git commit`, `git add`, `git push`, `git stash`, or any comman
 
 {{VERIFY_COMMANDS}}
 
-## Spec
+{{ORIGINAL_SPEC}}
 
 {{SPEC}}
 
diff --git a/src/draft/steps/implement_spec/original_spec.py b/src/draft/steps/implement_spec/original_spec.py
new file mode 100644
index 0000000..45993b1
--- /dev/null
+++ b/src/draft/steps/implement_spec/original_spec.py
@@ -0,0 +1,70 @@
+import os
+from importlib.resources import files
+from pathlib import Path
+
+from draft.runs import find_original_run_on_branch, load_state
+
+CASE_NONE = "none"
+CASE_PRIOR_RUN = "prior_run"
+CASE_OPEN_PR = "open_pr"
+CASE_COMMITS_ONLY = "commits_only"
+
+_CASE_FILES = {
+    CASE_PRIOR_RUN: "original_spec_prior_run.md",
+    CASE_OPEN_PR: "original_spec_open_pr.md",
+    CASE_COMMITS_ONLY: "original_spec_commits_only.md",
+}
+
+
+def _load_case_template(case: str) -> str:
+    return files("draft.steps.implement_spec").joinpath(_CASE_FILES[case]).read_text()
+
+
+def _render_case(case: str, mapping: dict) -> str:
+    template = _load_case_template(case)
+    for key, value in mapping.items():
+        template = template.replace(f"{{{{{key}}}}}", value)
+    return template
+
+
+def resolve_case(ctx) -> tuple[str, dict]:
+    if ctx.get("branch_source") != "existing":
+        return (CASE_NONE, {})
+    original_run = find_original_run_on_branch(ctx.get("project"), ctx.get("branch"))
+    if original_run is not None:
+        state = load_state(original_run)
+        spec_path = state.get("data", {}).get("spec") if state else None
+        if spec_path and Path(spec_path).is_file() and os.access(spec_path, os.R_OK):
+            return (
+                CASE_PRIOR_RUN,
+                {
+                    "ORIGINAL_SPEC_PATH": spec_path,
+                    "ORIGINAL_RUN_ID": original_run.name,
+                },
+            )
+    pr_url = ctx.get("pr_url")
+    if pr_url:
+        return (CASE_OPEN_PR, {"PR_URL": pr_url})
+    return (
+        CASE_COMMITS_ONLY,
+        {
+            "BRANCH": ctx.get("branch") or "",
+            "BASE_BRANCH": ctx.get("base_branch") or "origin/main",
+        },
+    )
+
+
+def render_original_spec(ctx) -> str:
+    case, mapping = resolve_case(ctx)
+    if case == CASE_NONE:
+        return ""
+    return _render_case(case, mapping)
+
+
+def preamble_label(ctx) -> str | None:
+    case, mapping = resolve_case(ctx)
+    if case == CASE_PRIOR_RUN:
+        return f"run {mapping['ORIGINAL_RUN_ID']}"
+    if case == CASE_OPEN_PR:
+        return f"PR {mapping['PR_URL']}"
+    return None
diff --git a/src/draft/steps/implement_spec/original_spec_commits_only.md b/src/draft/steps/implement_spec/original_spec_commits_only.md
new file mode 100644
index 0000000..f8b8d11
--- /dev/null
+++ b/src/draft/steps/implement_spec/original_spec_commits_only.md
@@ -0,0 +1,10 @@
+## Original spec
+
+No prior run or open PR was found. Review the branch commits for context.
+
+```bash
+git log {{BASE_BRANCH}}..HEAD --oneline
+git show <commit>
+```
+
+Branch: `{{BRANCH}}`
diff --git a/src/draft/steps/implement_spec/original_spec_open_pr.md b/src/draft/steps/implement_spec/original_spec_open_pr.md
new file mode 100644
index 0000000..f9dab23
--- /dev/null
+++ b/src/draft/steps/implement_spec/original_spec_open_pr.md
@@ -0,0 +1,9 @@
+## Original spec
+
+This branch has an open pull request. Review it to understand the original intent.
+
+```bash
+gh pr view {{PR_URL}}
+```
+
+PR: {{PR_URL}}
diff --git a/src/draft/steps/implement_spec/original_spec_prior_run.md b/src/draft/steps/implement_spec/original_spec_prior_run.md
new file mode 100644
index 0000000..ca02279
--- /dev/null
+++ b/src/draft/steps/implement_spec/original_spec_prior_run.md
@@ -0,0 +1,5 @@
+## Original spec
+
+This branch was started in run `{{ORIGINAL_RUN_ID}}` from the spec at:
+
+{{ORIGINAL_SPEC_PATH}}
diff --git a/tests/draft/test_code_spec.py b/tests/draft/test_code_spec.py
index cb33c5e..628635b 100644
--- a/tests/draft/test_code_spec.py
+++ b/tests/draft/test_code_spec.py
@@ -11,6 +11,7 @@
     _format_suggested_failures,
     _generate_commit_message,
     _load_template,
+    _log_prompt,
     _parse_suggestions,
     _render_prompt,
     _render_verify_commands,
@@ -120,7 +121,7 @@ def test_render_prompt_empty_verify_commands_collapses_marker(tmp_path):
 
     prompt = _render_prompt(ctx, template, "")
     assert "{{VERIFY_COMMANDS}}" not in prompt
-    assert "## Verify commands" not in prompt
+    assert "## Verified commands" not in prompt
 
 
 def test_render_prompt_template_without_verify_commands_marker(tmp_path):
@@ -179,7 +180,7 @@ def test_render_verify_commands_none_like_input():
 
 def test_render_verify_commands_single_entry():
     result = _render_verify_commands([{"cmd": "make test"}])
-    assert "## Verify commands" in result
+    assert "## Verified commands" in result
     assert "Run them yourself before finishing if practical" in result
     assert "```bash" in result
     assert "make test" in result
@@ -334,7 +335,7 @@ def test_run_prompt_contains_verify_commands_when_configured(tmp_path):
         step.run(ctx, engine, lifecycle, MagicMock())
 
     prompt = engine.run_llm.call_args[1]["prompt"]
-    assert "## Verify commands" in prompt
+    assert "## Verified commands" in prompt
     assert "make test" in prompt
 
 
@@ -1466,3 +1467,189 @@ def test_bundled_summarize_status_has_tail_placeholder():
         files("draft.steps.implement_spec").joinpath("summarize_status.md").read_text()
     )
     assert "{{TAIL}}" in content
+
+
+# --- heading rename tests ---
+
+
+def test_render_verify_commands_heading_is_verified_commands():
+    result = _render_verify_commands([{"cmd": "make lint"}])
+    assert result.startswith("## Verified commands")
+
+
+def test_render_prompt_verify_errors_section_uses_verified_errors_heading(tmp_path):
+    tpl = tmp_path / "tpl.md"
+    tpl.write_text("{{SPEC}}\n{{VERIFY_ERRORS}}")
+    template = tpl.read_text()
+
+    ctx = MagicMock()
+    ctx.get.return_value = "spec"
+    ctx.step_get.return_value = "some error"
+
+    prompt = _render_prompt(ctx, template, "")
+    assert "## Verified errors" in prompt
+    assert "## Test failures" not in prompt
+
+
+# --- _render_prompt four-placeholder tests ---
+
+
+def test_render_prompt_substitutes_spec_with_current_spec_heading(tmp_path):
+    tpl = tmp_path / "tpl.md"
+    tpl.write_text("{{SPEC}}")
+    template = tpl.read_text()
+
+    ctx = MagicMock()
+    ctx.get.return_value = "/path/to/spec.md"
+    ctx.step_get.return_value = ""
+
+    prompt = _render_prompt(ctx, template, "")
+    assert "## Current Spec" in prompt
+    assert "/path/to/spec.md" in prompt
+    assert "{{SPEC}}" not in prompt
+
+
+def test_render_prompt_never_contains_spec_placeholder():
+    bundled = _load_template({})
+    ctx = MagicMock()
+    ctx.get.return_value = "the spec"
+    ctx.step_get.return_value = ""
+
+    prompt = _render_prompt(ctx, bundled, "")
+    assert "{{SPEC}}" not in prompt
+    assert "## Current Spec" in prompt
+
+
+def test_render_prompt_substitutes_original_spec(tmp_path):
+    tpl = tmp_path / "tpl.md"
+    tpl.write_text(
+        "{{ORIGINAL_SPEC}}\n{{SPEC}}\n{{VERIFY_COMMANDS}}\n{{VERIFY_ERRORS}}"
+    )
+    template = tpl.read_text()
+
+    ctx = MagicMock()
+    ctx.get.side_effect = lambda key, default=None: {
+        "spec": "my-spec",
+        "branch_source": "existing",
+        "branch": "my-branch",
+        "project": "proj",
+        "base_branch": "origin/main",
+    }.get(key, default)
+    ctx.step_get.return_value = ""
+
+    from unittest.mock import patch
+
+    with patch(
+        "draft.steps.implement_spec.original_spec.render_original_spec",
+        return_value="## Original spec\n\nsome context",
+    ):
+        prompt = _render_prompt(ctx, template, "")
+
+    assert "## Original spec" in prompt
+    assert "some context" in prompt
+    assert "{{ORIGINAL_SPEC}}" not in prompt
+
+
+def test_render_prompt_custom_template_without_original_spec_still_runs(tmp_path):
+    tpl = tmp_path / "tpl.md"
+    tpl.write_text("{{SPEC}}\n{{VERIFY_ERRORS}}")
+    template = tpl.read_text()
+
+    ctx = MagicMock()
+    ctx.get.return_value = "spec-content"
+    ctx.step_get.return_value = ""
+
+    prompt = _render_prompt(ctx, template, "")
+    assert "spec-content" in prompt
+    assert "{{SPEC}}" not in prompt
+
+
+# --- _log_prompt tests ---
+
+
+def test_log_prompt_appends_bracketed_block(tmp_path):
+    log_path = tmp_path / "implement-spec.log"
+    _log_prompt(log_path, "my prompt text", attempt=1, max_attempts=3)
+    content = log_path.read_text()
+    assert "=== implement-spec prompt (attempt 1/3) @" in content
+    assert "my prompt text" in content
+    assert "=== end prompt ===" in content
+
+
+def test_log_prompt_two_retries_produce_two_blocks(tmp_path):
+    log_path = tmp_path / "implement-spec.log"
+    _log_prompt(log_path, "first prompt", attempt=1, max_attempts=2)
+    _log_prompt(log_path, "second prompt", attempt=2, max_attempts=2)
+    content = log_path.read_text()
+    assert content.index("attempt 1/2") < content.index("attempt 2/2")
+    assert "first prompt" in content
+    assert "second prompt" in content
+
+
+def test_log_prompt_oserror_prints_warning_and_continues(tmp_path, capsys):
+    log_path = tmp_path / "implement-spec.log"
+
+    with patch("builtins.open", side_effect=OSError("permission denied")):
+        _log_prompt(log_path, "prompt", attempt=1, max_attempts=1)
+
+    captured = capsys.readouterr()
+    assert "warning" in captured.err
+    assert "permission denied" in captured.err
+
+
+def test_log_prompt_called_before_run_llm(tmp_path):
+    cfg = {"max_retries": 1, "timeout": 60}
+    log_path = tmp_path / "implement-spec.log"
+    ctx = _make_ctx(cfg, tmp_path=tmp_path)
+    ctx.log_path.return_value = log_path
+    lifecycle = MagicMock()
+    lifecycle.run_hooks.return_value = []
+
+    call_order = []
+
+    def fake_log_prompt(*a, **kw):
+        call_order.append("log")
+
+    llm_result = MagicMock()
+    llm_result.rc = 0
+    llm_result.final_text = "commit msg"
+
+    def fake_run_llm(*a, **kw):
+        call_order.append("llm")
+        return llm_result
+
+    engine = MagicMock()
+    stage_ctx = MagicMock()
+    stage_ctx.__enter__ = MagicMock(return_value=MagicMock())
+    stage_ctx.__exit__ = MagicMock(return_value=False)
+    engine.stage.return_value = stage_ctx
+    engine.run_llm.side_effect = fake_run_llm
+
+    step = ImplementSpecStep()
+    with (
+        patch("draft.steps.implement_spec._has_changes", return_value=True),
+        patch(
+            "draft.steps.implement_spec._log_prompt", side_effect=fake_log_prompt
+        ) as mock_log,
+        patch(
+            "draft.steps.implement_spec._generate_commit_message",
+            return_value=("msg", False),
+        ),
+        patch("draft.steps.implement_spec._run_git_capture", return_value="sha\n"),
+        patch(
+            "draft.steps.implement_spec._run_git_capture_allow_fail",
+            return_value=subprocess.CompletedProcess([], 0, b"", b""),
+        ),
+    ):
+        step.run(ctx, engine, lifecycle, MagicMock())
+
+    assert call_order == ["log", "llm"]
+    mock_log.assert_called_once()
+
+
+# --- bundled template markers ---
+
+
+def test_bundled_implement_spec_has_original_spec_marker():
+    bundled = _load_template({})
+    assert "{{ORIGINAL_SPEC}}" in bundled
diff --git a/tests/draft/test_commands.py b/tests/draft/test_commands.py
index 0443fa7..6d671e4 100644
--- a/tests/draft/test_commands.py
+++ b/tests/draft/test_commands.py
@@ -3255,3 +3255,75 @@ def test_init_cli_has_init_subcommand():
     ci.register(subs)
     choices = subs.choices
     assert "init" in choices
+
+
+# --- command_create preamble emission ---
+
+
+def test_command_create_preamble_emitted_when_label_returned(capsys):
+    import sys
+    from unittest.mock import MagicMock, patch
+
+    ctx = MagicMock()
+
+    with patch(
+        "draft.steps.implement_spec.original_spec.preamble_label",
+        return_value="run 250101-120000",
+    ):
+        try:
+            from draft.steps.implement_spec import original_spec
+
+            label = original_spec.preamble_label(ctx)
+            if label:
+                print(f"original-spec: attached from {label}", file=sys.stderr)
+        except Exception:
+            pass
+
+    captured = capsys.readouterr()
+    assert "original-spec: attached from run 250101-120000" in captured.err
+
+
+def test_command_create_preamble_suppressed_when_resolver_raises(capsys):
+    import sys
+    from unittest.mock import MagicMock, patch
+
+    ctx = MagicMock()
+
+    with patch(
+        "draft.steps.implement_spec.original_spec.preamble_label",
+        side_effect=Exception("resolver boom"),
+    ):
+        try:
+            from draft.steps.implement_spec import original_spec
+
+            label = original_spec.preamble_label(ctx)
+            if label:
+                print(f"original-spec: attached from {label}", file=sys.stderr)
+        except Exception:
+            pass
+
+    captured = capsys.readouterr()
+    assert "original-spec" not in captured.err
+
+
+def test_command_create_preamble_silent_for_none_label(capsys):
+    import sys
+    from unittest.mock import MagicMock, patch
+
+    ctx = MagicMock()
+
+    with patch(
+        "draft.steps.implement_spec.original_spec.preamble_label",
+        return_value=None,
+    ):
+        try:
+            from draft.steps.implement_spec import original_spec
+
+            label = original_spec.preamble_label(ctx)
+            if label:
+                print(f"original-spec: attached from {label}", file=sys.stderr)
+        except Exception:
+            pass
+
+    captured = capsys.readouterr()
+    assert "original-spec" not in captured.err
diff --git a/tests/draft/test_original_spec.py b/tests/draft/test_original_spec.py
new file mode 100644
index 0000000..5f95f8a
--- /dev/null
+++ b/tests/draft/test_original_spec.py
@@ -0,0 +1,339 @@
+import json
+from unittest.mock import MagicMock, patch
+
+from draft.steps.implement_spec.original_spec import (
+    CASE_COMMITS_ONLY,
+    CASE_NONE,
+    CASE_OPEN_PR,
+    CASE_PRIOR_RUN,
+    preamble_label,
+    render_original_spec,
+    resolve_case,
+)
+
+
+def _make_ctx(
+    branch_source=None,
+    branch="my-branch",
+    project="myproject",
+    pr_url=None,
+    base_branch=None,
+):
+    ctx = MagicMock()
+    data = {
+        "branch_source": branch_source,
+        "branch": branch,
+        "project": project,
+        "pr_url": pr_url,
+        "base_branch": base_branch,
+    }
+    ctx.get.side_effect = lambda key, default=None: data.get(key, default)
+    return ctx
+
+
+def _make_run(runs_dir, project, run_id, state_data, sessions=None):
+    run_dir = runs_dir / project / run_id
+    run_dir.mkdir(parents=True)
+    state = {"data": state_data}
+    if sessions:
+        state["sessions"] = sessions
+    (run_dir / "state.json").write_text(json.dumps(state))
+    return run_dir
+
+
+# --- resolve_case ---
+
+
+def test_resolve_case_new_branch_returns_none():
+    ctx = _make_ctx(branch_source="new")
+    case, mapping = resolve_case(ctx)
+    assert case == CASE_NONE
+    assert mapping == {}
+
+
+def test_resolve_case_no_branch_source_returns_none():
+    ctx = _make_ctx(branch_source=None)
+    case, mapping = resolve_case(ctx)
+    assert case == CASE_NONE
+
+
+def test_resolve_case_existing_branch_prior_run_readable_spec(tmp_path):
+    spec_file = tmp_path / "spec.md"
+    spec_file.write_text("my spec")
+
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-120000",
+        {"branch": "my-branch", "branch_source": "new", "spec": str(spec_file)},
+        sessions=[{"started_at": "2025-01-01T12:00:00Z"}],
+    )
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, mapping = resolve_case(ctx)
+
+    assert case == CASE_PRIOR_RUN
+    assert mapping["ORIGINAL_SPEC_PATH"] == str(spec_file)
+    assert mapping["ORIGINAL_RUN_ID"] == "250101-120000"
+
+
+def test_resolve_case_existing_branch_prior_run_spec_deleted_has_pr(tmp_path):
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-120000",
+        {
+            "branch": "my-branch",
+            "branch_source": "new",
+            "spec": str(tmp_path / "gone.md"),
+        },
+    )
+
+    pr_url = "https://github.com/org/repo/pull/42"
+    ctx = _make_ctx(
+        branch_source="existing", branch="my-branch", project="myproject", pr_url=pr_url
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, mapping = resolve_case(ctx)
+
+    assert case == CASE_OPEN_PR
+    assert mapping["PR_URL"] == pr_url
+
+
+def test_resolve_case_existing_branch_no_prior_run_no_pr(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    ctx = _make_ctx(
+        branch_source="existing",
+        branch="my-branch",
+        project="myproject",
+        base_branch="origin/main",
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, mapping = resolve_case(ctx)
+
+    assert case == CASE_COMMITS_ONLY
+    assert mapping["BRANCH"] == "my-branch"
+    assert mapping["BASE_BRANCH"] == "origin/main"
+
+
+def test_resolve_case_commits_only_default_base_branch(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    ctx = _make_ctx(
+        branch_source="existing",
+        branch="my-branch",
+        project="myproject",
+        base_branch=None,
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, mapping = resolve_case(ctx)
+
+    assert case == CASE_COMMITS_ONLY
+    assert mapping["BASE_BRANCH"] == "origin/main"
+
+
+def test_resolve_case_picks_earliest_of_two_prior_runs(tmp_path):
+    spec_file = tmp_path / "spec.md"
+    spec_file.write_text("spec")
+
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-200000",
+        {"branch": "my-branch", "branch_source": "new", "spec": str(spec_file)},
+        sessions=[{"started_at": "2025-01-01T20:00:00Z"}],
+    )
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-080000",
+        {"branch": "my-branch", "branch_source": "new", "spec": str(spec_file)},
+        sessions=[{"started_at": "2025-01-01T08:00:00Z"}],
+    )
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, mapping = resolve_case(ctx)
+
+    assert case == CASE_PRIOR_RUN
+    assert mapping["ORIGINAL_RUN_ID"] == "250101-080000"
+
+
+def test_resolve_case_corrupt_json_skipped_falls_through_to_commits_only(tmp_path):
+    runs_dir = tmp_path / "runs"
+    run_dir = runs_dir / "myproject" / "250101-120000"
+    run_dir.mkdir(parents=True)
+    (run_dir / "state.json").write_text("not json{{{{")
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, _ = resolve_case(ctx)
+
+    assert case == CASE_COMMITS_ONLY
+
+
+def test_resolve_case_missing_branch_source_treated_as_non_match(tmp_path):
+    spec_file = tmp_path / "spec.md"
+    spec_file.write_text("spec")
+
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-120000",
+        {"branch": "my-branch", "spec": str(spec_file)},
+    )
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        case, _ = resolve_case(ctx)
+
+    assert case == CASE_COMMITS_ONLY
+
+
+# --- render_original_spec ---
+
+
+def test_render_original_spec_none_returns_empty_string():
+    ctx = _make_ctx(branch_source="new")
+    result = render_original_spec(ctx)
+    assert result == ""
+
+
+def test_render_original_spec_prior_run_contains_required_parts(tmp_path):
+    spec_file = tmp_path / "spec.md"
+    spec_file.write_text("spec content")
+
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-120000",
+        {"branch": "my-branch", "branch_source": "new", "spec": str(spec_file)},
+        sessions=[{"started_at": "2025-01-01T12:00:00Z"}],
+    )
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        result = render_original_spec(ctx)
+
+    assert "## Original spec" in result
+    assert str(spec_file) in result
+    assert "250101-120000" in result
+
+
+def test_render_original_spec_open_pr_contains_gh_pr_view(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    pr_url = "https://github.com/org/repo/pull/42"
+    ctx = _make_ctx(
+        branch_source="existing", branch="my-branch", project="myproject", pr_url=pr_url
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        result = render_original_spec(ctx)
+
+    assert "## Original spec" in result
+    assert f"gh pr view {pr_url}" in result
+    assert f"PR: {pr_url}" in result
+
+
+def test_render_original_spec_commits_only_contains_branch_and_git_log(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    ctx = _make_ctx(
+        branch_source="existing",
+        branch="my-branch",
+        project="myproject",
+        base_branch="origin/main",
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        result = render_original_spec(ctx)
+
+    assert "## Original spec" in result
+    assert "my-branch" in result
+    assert "git log origin/main..HEAD" in result
+
+
+def test_render_original_spec_commits_only_literal_commit_token(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        result = render_original_spec(ctx)
+
+    assert "<commit>" in result
+
+
+# --- preamble_label ---
+
+
+def test_preamble_label_new_branch_returns_none():
+    ctx = _make_ctx(branch_source="new")
+    assert preamble_label(ctx) is None
+
+
+def test_preamble_label_commits_only_returns_none(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        assert preamble_label(ctx) is None
+
+
+def test_preamble_label_prior_run_returns_run_id(tmp_path):
+    spec_file = tmp_path / "spec.md"
+    spec_file.write_text("spec")
+
+    runs_dir = tmp_path / "runs"
+    _make_run(
+        runs_dir,
+        "myproject",
+        "250101-120000",
+        {"branch": "my-branch", "branch_source": "new", "spec": str(spec_file)},
+        sessions=[{"started_at": "2025-01-01T12:00:00Z"}],
+    )
+
+    ctx = _make_ctx(branch_source="existing", branch="my-branch", project="myproject")
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        label = preamble_label(ctx)
+
+    assert label == "run 250101-120000"
+
+
+def test_preamble_label_open_pr_returns_pr_url(tmp_path):
+    runs_dir = tmp_path / "runs"
+    (runs_dir / "myproject").mkdir(parents=True)
+
+    pr_url = "https://github.com/org/repo/pull/42"
+    ctx = _make_ctx(
+        branch_source="existing", branch="my-branch", project="myproject", pr_url=pr_url
+    )
+
+    with patch("draft.runs.runs_base", return_value=runs_dir):
+        label = preamble_label(ctx)
+
+    assert label == f"PR {pr_url}"