…#58)

Hand-merged from anomalyco/opencode@dab2637217 ("fix(compaction):
adjust instructions and structure to be more clear to smaller models
like dsv4 flash", anomalyco#42045). Their patch didn't cherry-pick cleanly --
it conflicts with TKT-379 (the compaction summary must NOT hide that
context was compacted; hiding it measurably drops history_search's
call rate from 100% to 20%) and with our own splitPrefix/splitSuffix/
retainedCount extension to select(). Reapplied by hand, taking the
genuinely good parts and explicitly not the rest:

TAKEN:
- New SUMMARY_UPDATE_INSTRUCTIONS block: explicit guidance for
  combining a <prior-summary> with new <conversation> content
  (carry forward objectives/constraints/decisions, conversation wins
  on conflict, move Active->Completed, update Objective/Next Move).
- buildPrompt() restructured to wrap the actual conversation content
  in explicit <conversation> tags up front, before the instructions,
  instead of spreading context items loose at the end of the prompt
  array. This is the actual "clearer to smaller models" improvement.
- Tag renamed <previous-summary> -> <prior-summary> to match. Fixed
  every place that tag name is asserted or referenced, including in
  the SECOND compaction pipeline (packages/opencode/src/session/
  compaction.ts) that turns out to share this same buildPrompt() --
  and its own agent system prompt (packages/core/src/plugin/agent.ts
  PROMPT_COMPACTION / packages/opencode/src/agent/prompt/
  compaction.txt), which told the model to look for the old tag name.

NOT TAKEN, deliberately (Sean: "don't take their side"):
- Upstream's version of this same instruction says "Do not mention
  the summary process or that context was compacted" -- the exact
  opposite of TKT-379's fix. Kept our version unchanged. Added a
  test pinning this so a future upstream sync can't silently
  reintroduce it via a cleaner-looking cherry-pick.
- Upstream's select() also drops splitPrefix/splitSuffix (character-
  level splitting of a message straddling the retention boundary) in
  favor of whole-message-only slicing. Our fork extended that same
  logic with retainedCount (feeds
  SessionEvent.Compaction.Ended.retainedTailMessages) -- left
  entirely untouched.

NOT TOUCHED, flagged to feedback instead (anomalyco#227): PROMPT_COMPACTION's
own "do not mention... compacting" sentence (a second, separate
instance of the same class of bug TKT-379 fixed) and the
packages/core/src/v1/config/config.ts tail_turns docstring clarity
change -- both belong to the second compaction pipeline, whose
liveness relative to the first is TKT-377's still-open question, not
something to resolve as a side effect of this hand-merge.

Co-authored-by: opencode <bot@opencode.ai>
Co-authored-by: Claude <noreply@anthropic.com>

…hydration-fix

Sync 86 upstream commits (Aug 6-14) including:
- ID-wrap/chronological message ordering fixes (anomalyco#40987-anomalyco#41006) — upstream
  independently fixed the same bug class as our 07889a1/21964da41;
  adopted upstream versions (parentID === user.id for prompt exit, same
  findIndex boundaries for revert/session, isAfter helper in latest())
- v1.18.18 release (4 releases: v1.18.15-18)
- v1 database compatibility preservation (anomalyco#42444)
- ignore unknown config fields (anomalyco#41312)
- session retry cap with jitter (anomalyco#41939)
- compaction instructions for smaller models (anomalyco#42045)
- DeepSeek V4 Flash sampling defaults (anomalyco#41620)
- Copilot PDF input support detection (anomalyco#41522)
- web search for opencode-go (anomalyco#42630)
- compaction plugin hooks (experimental.session.compacting, messages.transform)
- New models: GLM 5.3, Gemini 3.7 Flash, Grok 4.6, Zen updates

Fork-only changes preserved:
- Synthetic web search backend (synthetic flag in webSearchEnabled)
- Config npm propagation to inherited models
- Tool-result media extraction for models without attachment capability
- packageManager pin to bun 1.4.-canary.1 (Rust runtime)

Conflicts resolved: message-v2, prompt, revert, session, server-session
(adopted upstream), compaction (adopted upstream), registry + websearch
test (merged both synthetic + opencode-go).

…+ anomalyco#42045)