T07: agentic realization over a stdlib browser surface

Two decisions taken with the operator: stdlib HTML driver instead of
Playwright (F-0004), and a deterministic discovery runtime instead of a live
model. Both sit behind interfaces so the alternatives drop in later.

- html.py: stdlib DOM parse and query
- agentic.py: DiscoveryRuntime (agentic arm, ignores data-td by construction)
  and RecordedSelectorRuntime (control arm, uses the strongest identifier the
  page offers)
- browser.py: per-actor sessions over real HTTP, constructed per call so no
  actor inherits another's connection state
- cost/nondeterminism metrics recorded from the first run

F-0005 (CONCEPT_DRIFT): the H-001 result is a narrowing. Where test ids are
preserved, discovery 9/9 and recorded selectors 9/9 - the semantic action buys
nothing. Where they are dropped, discovery 2/3 and recorded 0/3. The concept
model presents semantic actions as generally superior; the evidence says
conditionally superior.

M21 and M22 added mid-task: the deciding side of the axis was N=1. M22 (field
names renamed) defeats the heuristic and is the first concrete evidence that a
live model would add capability, not just cost.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1629012@bnt-lap001
Assistant-Session: 78d4fb13-8a1e-474b-87a3-9b9261c49a39

workplans/TD-WP-0002-vertical-spike-crystallization.md

@@ -307,7 +307,7 @@ fail*. All four `td://self/...` identifiers are covered. 72 tests pass overall.
 
 ```task
 id: TD-WP-0002-T07
-status: todo
+status: done
 priority: high
 state_hub_task_id: "b58cf7ce-dc18-5218-8eac-179291626467"
 ```
@@ -324,6 +324,36 @@ run than simply asking an agent to rewrite the broken test, the crystallization
 argument is an aesthetic preference rather than a value proposition. This data is
 free to collect from run one and impossible to backfill.
 
+**Done 2026-08-22.** `html.py` (stdlib DOM), `agentic.py` (two runtimes),
+`browser.py` (per-actor sessions over real HTTP), `scenarios/browser_grant.py`.
+107 tests pass. Two decisions taken with the operator: **stdlib HTML driver
+instead of Playwright** (F-0004) and **a deterministic discovery runtime instead
+of a live model**, both behind interfaces that let the alternatives drop in later.
+
+The headline result is a narrowing, not a confirmation:
+
+| | Discovery (agentic) | Recorded selectors (control) |
+|---|---|---|
+| test ids preserved (9 mutations) | 9/9 | **9/9** |
+| test ids dropped (3 mutations) | 2/3 | 0/3 |
+
+- **F-0005 — semantic actions earn their keep more narrowly than claimed.** Where
+  an application keeps stable identifiers, the conventional approach matches the
+  agentic one exactly and is cheaper, faster and deterministic. The semantic
+  action wins only where identifiers are absent or not carried forward. Filed as
+  `CONCEPT_DRIFT`: the concept model overstates this and should be revised to
+  match the evidence. Three mutations on the deciding side is directionally clear
+  and statistically nothing — recorded rather than rounded up.
+- **M22 marks where a scripted runtime stops.** Renaming form fields defeats the
+  heuristic, but the page still carries a "Person" label a model could read. This
+  is the first concrete evidence that a live model would add *capability* rather
+  than only cost — worth more than the general argument that it might.
+- Two mutations (M21, M22) were added mid-task because the deciding side of the
+  test-id axis was N=1 after the first run. Extending the instrument when the
+  evidence shows it is too thin is the intended behaviour.
+- Recovery happened with **no claim or invariant diff in any run**, and the one
+  failure failed *loudly* — `RealizationFailed` in evidence, not a silent pass.
+
 ## Adaptation detection and the defect-vs-adaptation classifier
 
 ```task